This strategy is valid for more or less all difficulty levels below deity, and does not rely on an amazing start position. I won't really make comments on specific difficulty levels much, as the map type and settings heavily influence the true difficulty of the game, and people have varying degrees of tolerance for regenerating the map to get a good start. I'm going to ignore Deity though, because I do not think OCC can be won consistently at that level without rigging the map (via playing islands or repeatedly regenerating for an incredible start) or using non-standard settings such as Permanent Alliances. And trying to build Pyramids on deity can be pretty frustrating too.
1) Pre-game show and overall strategy
First, let's consider the main difficulties in an OCC game.
Health cap: Unhappiness quickly goes away after the opening of the Globe Theatre. Health, however, is a constant issue as an OCC player can only control resources near her city. Forge, ironworks, lab, factory and coalplant cause unhealthiness too.
Research and production: How can we beat out opponents with ten cities when health stops us even growing to maximum size ourselves? The answer is in having free citizens that cost no food and don't contribute towards health. Enter the super specialist. A great engineer provides as much production as a citizen working a railroaded lumbermill, and provides as much research as a river town under representation! Tempting as it may be, you should NOT rush wonders with them, except maybe for the Space Elevator right at the end of the game. In a dedicated space race game you are taking a long term view to accumulate a certain amount of beakers towards the end of the game.
With this in mind we can evaluate the various traits. Philosophical is clearly very good getting you ~5 more super specialists throughout the course of the game. Industrious helps you build wonders (including national wonders, but not spaceship parts.) No other trait approaches these two. Unfortunately you can't have both together because the combination would be overpowered. Expansive tends to increase your population cap by 3 for most of the game and I think it's a very good choice for the second trait. Financial is decent, but there is a lot less space in OCC to use cottages as you want to keep a lot of forest for health and also to run Specialists. It works out well if you started out in a heavy calendar resource area. Unfortunately this isn't very common so I have to give Expansive the nod in general. Spiritual is really a diplomat's trait and diplomatic victories are outside the scope of this guide. The rest of the traits are pointless for OCC space race, and there's no need to dismiss them one by one.
Therefore the two leaders I recommend are Bismarck (Ind/Exp) and Peter (Phi/Exp). Lately I have been preferring Peter, because the pyramids are relatively easy to get on OCC without industrious or stone anyway as you are not slowed down by building a settler. In Warlords, the Russian unique lab with 2 free scientists is also a rather nice bonus.
Either way the game tends to flow in similar patterns, although there are a few branch points where you can go down different paths. The most important thing to have at the start is NOT gold or stone as most people believe, but food. Ideally you should have two food resources or at least 1 + flood plains. If you have anything else in addition to this, it's a bonus. Being coastal, preferably on an inlet where not too many fat cross tiles are taken up by water, is always nice for harbours.
2) Ancient era and Wonder strategy
Grab the worker techs to improve your local resources, then Masonry for an early start on the Pyramids and Wheel/Bronze so your worker has something constructive to do. Forests outside the city radius can be chopped to speed the pyramids, try to save some forests within the city radius for health and lumbermills later though. If you're missing both horses and bronze, a common OCC problem, go ahead and get archery so you can defend against barbarian pillaging. Both Bismarck and Peter start with hunting anyway so it's not much of a detour. Guerilla Archers on hills are a good defence against barbarian axes.
Pyramids are much better than Oracle/CS slingshot for this strategy. Bureaucracy doesn't work on specialist research, and great engineer points are a lot more desirable than prophet ones. I would not try to get the oracle in addition to the pyramids once you go past prince, it's too unreliable to try for both. Parthenon should be avoided too, even if you are industrious. +50% GPP until chemistry isn't worth polluting the gene pool with more great artists until the end of time. Just wait for the greatly superior national epic.
Normally I go for:
Pyramids
Great Library
Hanging Gardens (health + GE points)
National Epic
Globe Theatre
Oxford University
Ironworks (because we can trade for iron and coal)
Broadway (for resource trades)
Rock and Roll (for resource trades)
Internet (might not be as useful on low difficulties)
Space Elevator
I build Hagia Sophia and Pentagon for the GE points if I have nothing more important to build when I trade for their enabling techs.
I avoid parthenon, heroic epic (this is a peaceful strategy) and Taj Mahal like the plague, their effects are simply not worth the extra great artist pollution for this strategy. Broadway and Rock and Roll are tolerable because they come in the late game. I avoid the merchant and priest wonders too, as gold is fairly useless.
3) Diplomacy
I often stay agnostic and don't adopt a state religion in order not to antagonize neighbours. Being invaded and pillaged is not usually fatal, but is very disruptive. If all the neighbours are the same religion and it spreads though, Org Rel and Pacifism are useful civics. I would not recommend founding a religion yourself because in an OCC game that makes it very difficult to acquire neighbours' religions.
It's ok to give in to early game tribute demands and cancel them after 10 turns to keep relations up with future potential trading partners. That's what I view the other civs as. Trading partners to get the resources you're missing.
4) Into the Medieval
As previously mentioned you want great library and if you can get it, Hanging gardens. Gardens are often built late by the AI, and in addition to the immediate +1 health benefit act as another GE source. You'll be getting alphabet en route to literature. Resist the temptation to trade for every missing ancient tech, as this will make the AIs reluctant to trade more valuable techs with you later. Trade for mathematics and iron working to save time, maybe sailing or something. Research things like meditation yourself, it doesn't take long.
Civil service (for production) and Drama (for happiness control) usually become priorities after literature at this point. Usually I would go for civil service first unless stuck at size 6 due to lack of happiness resources/trades. Note, there is no big rush to build the globe theatre, as it adds extra artists to the gene pool early. It is OK to just build a regular theatre and run a bit of culture slider, as the vast majority of your research will be coming from specialists at this point anyway. I often build great library, hanging gardens, national epic first before coming back to Globe. Once Globe is done, all happiness resources can be traded away for health ones allowing the city to grow.
The research order is not set in stone, and if there are some useful resources in the 5th ring it's quite reasonable to take a detour to Music to get the artist for a quick culture bomb. Likewise philosophy for Pacifism can be useful - if you have religion AND the diplomatic situation allows you to run it. Being attacked by AIs is a pain, it's very disruptive even if not fatal.
After these are done, it's best to run straight to education and watch your research beakers shoot up due to Oxford. If no one has the liberalism prereqs you can switch from liberalism to something else with 1 turn to go to try and squeeze as big a tech out as possible. Trade for the Guilds side of the tree if possible and run an Engineer specialist once you have a forge, to increase the number of GE sources.
5) Industrial age and the Scientific Method dilemma
Don't put off scientific method too long. It's true you can research a lot of techs while avoiding scientific method to preserve the great library for a while more, but often these techs can also be traded for and thus obtained for free. If production looks like it might be a problem though, go ahead and get replaceable parts or steel early. It is likely that you are approaching the point of diminishing GPP returns by now anyway.
Going scientific method early will ensure a free great scientist at Physics which somewhat makes up for the loss of the great library.
Biology can be somewhat tempting at this point if you're running several farms, and medicine one tech away from that will solve all health problems. The main trouble with medicine is it takes 10+ turns to research a tech that isn't on the spaceship path which can come back to bite you in the end. So I prefer to build both Broadway and Rock and Roll to get plenty of resources for trading. Trading both hit resources as a package will also generally get a strategic resource such as iron, coal, aluminium or copper in exchange and I've found it to be the most reliable way to ensure you can get access to these (Short of blatant cheating by peeking in the map editor.)
And all these techs (physics, electricity and radio) are on the way to computers giving you the last research enhancer. Great if you're playing Peter under Warlords.
6) Building the spaceship
Towards the endgame the AI will typically refuse to trade anything above rocketry because 'We'd rather win the game, thanks', and their large land area combined with Biology/Representation begins to pull them ahead of the player in research beakers per turn. The endgame techs are very expensive and research is usually the bottleneck - it's quite common for fusion to take up to 15 turns for a cottage-light OCC. You can still get some techs free via the Internet, so after Computers I'll generally head for Fibre Optics via Rocketry/Apollo, and try to trade for Assembly Line along the way. In a close game the Internet will often pull in techs like industralism, plastics, robotics saving many turns of research, as the computer usually takes this path while I research fusion. Definitely worth taking a break from spaceship parts for a bit in most games as research is the bottleneck. The computer never builds internet so don't worry about being beaten to it.
If open I'll then build space elevator using the Fusion engineer to finish it. It doesn't save many turns because a lot of Casings and things have already been built, but it's usually worth keeping it out of AI hands anyway.
The last two techs are typically genetics and ecology, giving the AI maximum time to give biology and refrigeration for free via the internet.
Enjoy. I've been mainly testing at emperor and you don't need gold or anything like that. 2 food is enough, and fairly common. Immortal requires some luck as there are often runaway AIs and you may need to stir the pot a bit more by starting inter-AI wars. Just try not to antagonize civs to the point where they won't trade with you, you never know who's going to have the coal/aluminium.
1) Pre-game show and overall strategy
First, let's consider the main difficulties in an OCC game.
Health cap: Unhappiness quickly goes away after the opening of the Globe Theatre. Health, however, is a constant issue as an OCC player can only control resources near her city. Forge, ironworks, lab, factory and coalplant cause unhealthiness too.
Research and production: How can we beat out opponents with ten cities when health stops us even growing to maximum size ourselves? The answer is in having free citizens that cost no food and don't contribute towards health. Enter the super specialist. A great engineer provides as much production as a citizen working a railroaded lumbermill, and provides as much research as a river town under representation! Tempting as it may be, you should NOT rush wonders with them, except maybe for the Space Elevator right at the end of the game. In a dedicated space race game you are taking a long term view to accumulate a certain amount of beakers towards the end of the game.
With this in mind we can evaluate the various traits. Philosophical is clearly very good getting you ~5 more super specialists throughout the course of the game. Industrious helps you build wonders (including national wonders, but not spaceship parts.) No other trait approaches these two. Unfortunately you can't have both together because the combination would be overpowered. Expansive tends to increase your population cap by 3 for most of the game and I think it's a very good choice for the second trait. Financial is decent, but there is a lot less space in OCC to use cottages as you want to keep a lot of forest for health and also to run Specialists. It works out well if you started out in a heavy calendar resource area. Unfortunately this isn't very common so I have to give Expansive the nod in general. Spiritual is really a diplomat's trait and diplomatic victories are outside the scope of this guide. The rest of the traits are pointless for OCC space race, and there's no need to dismiss them one by one.
Therefore the two leaders I recommend are Bismarck (Ind/Exp) and Peter (Phi/Exp). Lately I have been preferring Peter, because the pyramids are relatively easy to get on OCC without industrious or stone anyway as you are not slowed down by building a settler. In Warlords, the Russian unique lab with 2 free scientists is also a rather nice bonus.
Either way the game tends to flow in similar patterns, although there are a few branch points where you can go down different paths. The most important thing to have at the start is NOT gold or stone as most people believe, but food. Ideally you should have two food resources or at least 1 + flood plains. If you have anything else in addition to this, it's a bonus. Being coastal, preferably on an inlet where not too many fat cross tiles are taken up by water, is always nice for harbours.
2) Ancient era and Wonder strategy
Grab the worker techs to improve your local resources, then Masonry for an early start on the Pyramids and Wheel/Bronze so your worker has something constructive to do. Forests outside the city radius can be chopped to speed the pyramids, try to save some forests within the city radius for health and lumbermills later though. If you're missing both horses and bronze, a common OCC problem, go ahead and get archery so you can defend against barbarian pillaging. Both Bismarck and Peter start with hunting anyway so it's not much of a detour. Guerilla Archers on hills are a good defence against barbarian axes.
Pyramids are much better than Oracle/CS slingshot for this strategy. Bureaucracy doesn't work on specialist research, and great engineer points are a lot more desirable than prophet ones. I would not try to get the oracle in addition to the pyramids once you go past prince, it's too unreliable to try for both. Parthenon should be avoided too, even if you are industrious. +50% GPP until chemistry isn't worth polluting the gene pool with more great artists until the end of time. Just wait for the greatly superior national epic.
Normally I go for:
Pyramids
Great Library
Hanging Gardens (health + GE points)
National Epic
Globe Theatre
Oxford University
Ironworks (because we can trade for iron and coal)
Broadway (for resource trades)
Rock and Roll (for resource trades)
Internet (might not be as useful on low difficulties)
Space Elevator
I build Hagia Sophia and Pentagon for the GE points if I have nothing more important to build when I trade for their enabling techs.
I avoid parthenon, heroic epic (this is a peaceful strategy) and Taj Mahal like the plague, their effects are simply not worth the extra great artist pollution for this strategy. Broadway and Rock and Roll are tolerable because they come in the late game. I avoid the merchant and priest wonders too, as gold is fairly useless.
3) Diplomacy
I often stay agnostic and don't adopt a state religion in order not to antagonize neighbours. Being invaded and pillaged is not usually fatal, but is very disruptive. If all the neighbours are the same religion and it spreads though, Org Rel and Pacifism are useful civics. I would not recommend founding a religion yourself because in an OCC game that makes it very difficult to acquire neighbours' religions.
It's ok to give in to early game tribute demands and cancel them after 10 turns to keep relations up with future potential trading partners. That's what I view the other civs as. Trading partners to get the resources you're missing.
4) Into the Medieval
As previously mentioned you want great library and if you can get it, Hanging gardens. Gardens are often built late by the AI, and in addition to the immediate +1 health benefit act as another GE source. You'll be getting alphabet en route to literature. Resist the temptation to trade for every missing ancient tech, as this will make the AIs reluctant to trade more valuable techs with you later. Trade for mathematics and iron working to save time, maybe sailing or something. Research things like meditation yourself, it doesn't take long.
Civil service (for production) and Drama (for happiness control) usually become priorities after literature at this point. Usually I would go for civil service first unless stuck at size 6 due to lack of happiness resources/trades. Note, there is no big rush to build the globe theatre, as it adds extra artists to the gene pool early. It is OK to just build a regular theatre and run a bit of culture slider, as the vast majority of your research will be coming from specialists at this point anyway. I often build great library, hanging gardens, national epic first before coming back to Globe. Once Globe is done, all happiness resources can be traded away for health ones allowing the city to grow.
The research order is not set in stone, and if there are some useful resources in the 5th ring it's quite reasonable to take a detour to Music to get the artist for a quick culture bomb. Likewise philosophy for Pacifism can be useful - if you have religion AND the diplomatic situation allows you to run it. Being attacked by AIs is a pain, it's very disruptive even if not fatal.
After these are done, it's best to run straight to education and watch your research beakers shoot up due to Oxford. If no one has the liberalism prereqs you can switch from liberalism to something else with 1 turn to go to try and squeeze as big a tech out as possible. Trade for the Guilds side of the tree if possible and run an Engineer specialist once you have a forge, to increase the number of GE sources.
5) Industrial age and the Scientific Method dilemma
Don't put off scientific method too long. It's true you can research a lot of techs while avoiding scientific method to preserve the great library for a while more, but often these techs can also be traded for and thus obtained for free. If production looks like it might be a problem though, go ahead and get replaceable parts or steel early. It is likely that you are approaching the point of diminishing GPP returns by now anyway.
Going scientific method early will ensure a free great scientist at Physics which somewhat makes up for the loss of the great library.
Biology can be somewhat tempting at this point if you're running several farms, and medicine one tech away from that will solve all health problems. The main trouble with medicine is it takes 10+ turns to research a tech that isn't on the spaceship path which can come back to bite you in the end. So I prefer to build both Broadway and Rock and Roll to get plenty of resources for trading. Trading both hit resources as a package will also generally get a strategic resource such as iron, coal, aluminium or copper in exchange and I've found it to be the most reliable way to ensure you can get access to these (Short of blatant cheating by peeking in the map editor.)
And all these techs (physics, electricity and radio) are on the way to computers giving you the last research enhancer. Great if you're playing Peter under Warlords.
6) Building the spaceship
Towards the endgame the AI will typically refuse to trade anything above rocketry because 'We'd rather win the game, thanks', and their large land area combined with Biology/Representation begins to pull them ahead of the player in research beakers per turn. The endgame techs are very expensive and research is usually the bottleneck - it's quite common for fusion to take up to 15 turns for a cottage-light OCC. You can still get some techs free via the Internet, so after Computers I'll generally head for Fibre Optics via Rocketry/Apollo, and try to trade for Assembly Line along the way. In a close game the Internet will often pull in techs like industralism, plastics, robotics saving many turns of research, as the computer usually takes this path while I research fusion. Definitely worth taking a break from spaceship parts for a bit in most games as research is the bottleneck. The computer never builds internet so don't worry about being beaten to it.
If open I'll then build space elevator using the Fusion engineer to finish it. It doesn't save many turns because a lot of Casings and things have already been built, but it's usually worth keeping it out of AI hands anyway.
The last two techs are typically genetics and ecology, giving the AI maximum time to give biology and refrigeration for free via the internet.
Enjoy. I've been mainly testing at emperor and you don't need gold or anything like that. 2 food is enough, and fairly common. Immortal requires some luck as there are often runaway AIs and you may need to stir the pot a bit more by starting inter-AI wars. Just try not to antagonize civs to the point where they won't trade with you, you never know who's going to have the coal/aluminium.