HOUSTON — Over the past two years, environmentalists have chained themselves to the White House fence and otherwise coalesced around stopping the Keystone XL pipeline as their top priority in the fight against global warming.

But even if President Obama rejects the pipeline, it might not matter much. Oil companies are already building rail terminals to deliver oil from western Canada to the United States, and even to Asia.

Since July, plans have been announced for three large loading terminals in western Canada with the combined capacity of 350,000 barrels a day — equivalent to roughly 40 percent of the capacity of the proposed Keystone XL pipeline that is designed to bring oil from western Alberta to refineries along the Gulf Coast.

Over all, Canada is poised to quadruple its rail-loading capacity over the next few years to as much as 900,000 barrels a day, up from 180,000 today.