HOUSTON (Reuters) -Top U.S. oil producers Exxon Mobil and Chevron are expected to report their lowest earnings in four years when they release second-quarter results on Friday, as weaker oil and gas prices slashed revenue.

The April-June quarter covered a volatile period in which the OPEC+ group of producers continued raising their production volumes, putting pressure on crude prices and in turn cutting the profits of oil firms. Oscillating tariff policy from U.S. President Donald Trump's administration also added to fears about weakening economies and oil demand. 

Global benchmark Brent crude prices declined 11% during the quarter from the previous three months, while U.S. natural gas futures declined 9%. 

While investors had previously been watching whether producers would cut spending in response to lower prices, the market is now likely to focus more on company-specific results and commentary about the macroeconomic environment, said Jeoffrey Lambujon, an analyst with TPH Energy Research, in a note last week. 

Exxon, the top U.S. oil producer, is expected to post $6.67 billion in adjusted earnings for the second quarter, or $1.56 per share, according to the consensus analyst estimates compiled by LSEG. 

That would be a 27% drop from the year-ago quarter and the lowest earnings since 2021, after the COVID-19 pandemic sank global demand. 

The company had signaled earlier this month that lower oil and gas prices could cut about $1.5 billion from its earnings compared with the first quarter.

One bright spot is improved refining margins, which Exxon said could help boost second-quarter earnings by about $300 million, but refining is a smaller portion of its business compared with oil and gas production.  

The company has several projects slated for start-up in the second half of the year that should drive stronger earnings, said Jason Gabelman, an analyst with TD Cowen in a July 10 research note. 

These include Yellowtail, a fourth floating production, storage and offloading vessel in the prolific Stabroek Block in Guyana, the lucrative oil hotspot where profits soared 64% last year. 

Wall Street expects Chevron, the No.2 U.S. oil producer, to report $3 billion in adjusted earnings, or $1.70 per share, down 33% from the same period a year ago and also the lowest in four years.

Chevron closed its acquisition of smaller oil producer Hess on July 18 after triumphing in a legal challenge from Exxon that delayed the deal close by over a year.

Chevron said the deal will lead to $1 billion in cost synergies by the end of the year. It will provide updated financial guidance for the combined company during its investor day in November. 

The company could report about 1% lower production volumes compared with the first quarter following a well blowout in Colorado, and a two-week production shutdown at the Leviathan gas field in Israel during the country's conflict with Iran, said Barclays analysts in a July 13 note. 

French oil major TotalEnergies last week reported its lowest profit in four years as higher production was not enough to make up for lower oil prices.

On Thursday, British oil major Shell reported a profit that tumbled by almost a third. Rival BP will release results next week.