Originally posted by State Machine
Rubber and oil are a bit odd. Their value is only after certain techs are researched. But, they get produced long before that based on scenario starting conditions and such.
This makes sense, though, since both were being produced as consumer products long before there was a military use. For example, rubber was first used to make canvas waterproof (the "mackintosh") in 1824, but even solid rubber tires weren't used until 1869, much less the air-filled (pneumatic) tire (1889, and whew! what a better ride on that bicycle). Likewise with oil, which was used for lighting (kerosene) long before it got refined into gasoline or was used for internal combustion engines (1860s-1890s, depending on which history you use... not widely available, though, until the late 1890s).