"Exxon and Occidental have the largest capacity for acquisitions among the biggest oil companies with US exposure," Bloomberg Intelligence said.

"Exxon would have as much as $35 billion in cash available for M&A, and still retain its credit rating. The numbers exclude equity issuance, which would raise war chests yet further."

The margin squeeze on the US shale oil scene is also worsening as oil hedges struck last year, which guaranteed minimum prices of $90 a barrel or more, are increasingly expiring with hedge prices now in the low $60s or worse.

"Interest in US shale play operators may increase if larger companies prefer to move to projects with smaller lead times," Bloomberg Intelligence commented in its report yesterday.

According to Bloomberg Intelligence's energy companies debt capacity calculator, Exxon had $35.56 billion of capacity for M&A while Chevron had $10.04 billion, Occidental had $3.6 billion, BP had $21.7 billion and Total had $13.3 billion.

Of these companies BP had the highest balance sheet cash position of $32.4 billion, followed by Total ($25 billion) and Chevron ($12.7 billion).