War isnt generally profitable for the government, but it is for the corperations.
As with oil, sure it may be only a portion of your oil (but 25% is still a huge amount of oil) but its still important. But even more so then guarentting you a cheap supply of oil, you can prevent your enemies from getting it. Oil drives economies and militaries. without it neither can function. China at the moment is fairly dependent on Middle eastern oil, although they are looking to get mroe from places like Russia, Canada, Kazekstan and other places.
While they are dependent on ME oil right now, control that supply and you can choke the Chinese economy.