US energy firms signed a series of multi-billion-dollar deals with Venezuela on Wednesday, days after the South American country agreed to grant Washington control of a huge chunk, roughly one-fifth, of its vast oil reserves.

US Energy Secretary Chris Wright travelled to Venezuela’s capital Caracas to oversee the signing of deals worth "tens of billions of dollars of investment," seen as a quid pro quo for Washington winning majority control of 65 billion barrels of Venezuelan oil reserves.

Wright said the deals signed by Venezuela with US oil major Chevron, GE Vernova – a General Electric offshoot – and Italy's ENI were "critical in starting this ball rolling of peace, opportunity, and prosperity" in the country.

US President Donald Trump has talked up the agreement on Venezuela's oil reserves as the "biggest oil deal in world history."

It comes as US Republicans brace for possible losses in November midterm elections due to spiralling fuel costs brought on by his war against Iran, and a broader national affordability crisis in housing, food, utilities and other basic needs.