India, Oct. 21 -- US secretary of state Marco Rubio said in Mumbai on Tuesday he would encourage Reliance Industries, which runs the Jamnagar refining complex in Gujarat, to refine more Venezuelan crude.

Behind the request is a complex set of immediate circumstances - particularly, multiple theatres of conflict that have driven oil prices, and in turn pump rates around the world, to uncomfortable levels. But a more fundamental factor is how crude oil, once nicknamed black gold, varies from one oilfield to the next, and how refineries that turn it into fuel are set up to handle a specific range and type of it.

Crude oil comes in varieties. Some of it is thin and runny. Merey, Venezuela's main export blend, is thick and slow-moving, more ...