Exxon Mobil Corp.Royal Dutch Shell PLC, BP PLC and Chevron Corp. hold a combined net debt of $184 billion -- more than double their debt levels in 2014, when oil prices began a steep descent that eventually bottomed out at $27 a barrel earlier this year. Crude prices have rebounded since, but still hover near $50 a barrel.

In common with other oil companies, the European trio are looking to divest non-core assets to help shore up their balance sheets and defend dividends at a time of mounting pressure from the prolonged weakness in oil prices.

The aggregate net debt of the 15 largest North American and European oil groups rose to $383bn at the end of March, up $97bn from 12 months ago.

The impact of weaker prices is being compounded by lower profits from refining, a business that has been bailing out oil majors over the past couple of years. Global refining margins dropped to $10.50 a barrel in the first quarter, 31 percent lower than a year earlier and 20 percent lower than the preceding quarter.