New Delhi, Jan. 6 -- President Donald Trump wants U.S. companies to rebuild Venezuela's oil industry, but Venezuelan oil can't simply be turned back on.

The country has vast reserves, estimated at roughly 303 billion barrels, the largest total in the world. Chevron, Exxon Mobil, and ConocoPhillips have long histories in the country, though only Chevron operates there now. In theory, those companies could turn Venezuela into a gusher, ramping up the country's production of 1 million barrels a day now.

The reality is that it wouldn't be easy for logistical, operational, and political reasons. Here's a look at Venezuelan oil and what it would take to get the crude flowing.

The most important patch is called the Orinoco Oil Belt, a vast ea...