S&P/ASX 200 Index (ASX: XJO) energy shares are having a day to forget.

During the Monday lunch hour, the ASX 200 is down 0.8%. But Australia's oil and gas companies are under heavier selling pressure, with the S&P/ASX 200 Energy Index (ASX: XEJ) down a far steeper 2.4%.

Here's how these top ASX 200 energy shares are performing at the time of writing:

• Woodside Energy Group Ltd (ASX: WDS) shares are down 3.4% at $19.92
• Santos Ltd (ASX: STO) shares are down 3.3% at $5.88
• Beach Energy Ltd (ASX: BPT) shares are down 3.3% at $1.16
• Karoon Energy Ltd (ASX: KAR) shares are down 2.9% at $1.42

Investors looking for someone to blame for today's sell-off need look no further than the Organization of the Petroleum Exporting Countries and its allies (OPEC+).

Here's what's happening.

OPEC's unwelcome move for ASX 200 energy shares

ASX 200 energy shares are feeling the pain amid another big pullback in global oil prices.

The Brent crude oil price is down 3.4% at US$59.20 per barrel. That sees Brent crude oil prices down 11% since last Monday.

This comes following Saturday's OPEC+ members video meeting. Saudi Arabia's Prince Abdulaziz bin Salman used the meeting to announce that the cartel would up its oil production by 400,000 barrels per day, commencing in June.

The shock announcement came just a month after OPEC+ rattled oil markets – and ASX 200 energy shares – with a similar output hike statement.

Analysts believe Saudi Arabia is fed up with cutting its own output to support oil prices, even as some other OPEC members continue to pump more oil than their allotted quotas.

Bob McNally, president of Rapidan Energy Advisers, pointed out this isn't the first time the Saudis have tried to punish other members for cheating on their quotas and get that back into line.

"A deliberate 'sweating' to instil discipline has occurred twice since 2014, roughly five years apart, and both episodes continued until group cohesion was restored," McNally said (quoted by Bloomberg).

Russia's energy representative, Alexander Novak, said there is a lot more oil on tap than is currently being pumped. According to Novak:

Russia, Saudi Arabia, the United Arab Emirates and Kuwait could all produce much more today. And we have potential projects and their development plans, but we are holding back production.

The Donald Trump factor

If you thought you could end this article without United States President Donald Trump rearing his head, I'll have to disappoint you.

Along with pushing for more domestic drilling and production ("Drill baby, drill!"), Trump has been pushing OPEC+ to lift output in order to get energy prices down.

"With this move Saudi Arabia is seeking to punish lack of compliance particularly from Kazakhstan but also ingratiate with President Trump's push for lower oil prices" Jorge Leon, an analyst at Rystad Energy, said (quoted by Bloomberg).

While that will come as good news to motorists and energy-intensive companies, slumping oil prices have been hammering ASX 200 energy shares like Woodside and Santos this year.