ExxonMobil is considering scaling up plans for a multibillion-dollar expansion of its Beaumont, Texas, oil refinery to make it one of the largest in the world, according to sources familiar with the plans.

Since at least last summer, Exxon has been quietly contemplating a major project to expand Beaumont in what would be the biggest US refinery investment since the shale revolution, which has transformed the country into a growing producer and handed refiners a profit windfall of cheap crude.

Initially the company was considering doubling the current 344,600-barrel-per-day (bpd) capacity by 2020, Reuters reported last year. Now it may go as high as 850,000 bpd by the end of the decade, according to the sources, a figure that would make it the largest US plant and fourth-largest in the world.

The latest details of the expansion plan, on which it has not made a final decision, emerged from Exxon’s campaign for a longer-than-usual term for the contract with the United Steelworkers union (USW) at the refinery.

Exxon has offered a minimum six-year contract consisting of the current four-year agreement negotiated earlier this month by the national union and US refiners, plus two more years, according to the company. The USW has countered with a proposal that would assure no work stoppages during the current national agreement and in the next national agreement, which is expected to be three to four years in length.

'Exxon Mobil regularly evaluates its global portfolio of businesses and opportunities for growth, depending upon the fit with its strategic business objectives,' said Exxon spokesman Lee Dula.

The Beaumont refinery was once a major importer of light or medium sour crudes from countries such as Saudi Arabia and Mexico, according to US government data, but has replaced much of that oil with domestic shale in recent years.