Last week's OPEC agreement reached at the Algiers conference to cut oil production caught the market by surprise. In the aftermath, prices have waxed and waned but reached highs for the week on Monday, even as there has been skepticism about whether OPEC's tentative deal will hold.

December Brent Crude contracts were up 1.4% or 70 cents to close at $50.89 a barrel on the London ICE futures exchange, the highest futures price in about six weeks.

November West Texas Intermediate was up 1.2% or 57 cents on the New York Merc, ending at $48.81 a barrel as it swung between lows of below $48 and highs above $49.

The OPEC pact calls for cuts to the group's output of between 32.5 million and 33 million barrels a day, down from the levels of 33.2 million barrels a day in August.

While the cap was eye-catching, Phillips Futures energy analyst Jonathan Chan stated, "OPEC has no way of enforcing the quotas." Iraq has already expressed skepticism about the production cuts and Russia's buy-in is anything but predictable. Production levels will be a topic for discussion at OPEC's next meeting in Vienna on November 30.

Even if the OPEC quotas experiences some slippage, however, one market analyst said "OPEC has at least built themselves what appears to be a (production) floor. No one thought they would get this done."

BMI Research forecasts decline in Saudi Arabia of about 360,000 barrels a day between August and November. The output by Saudis, OPEC's biggest producer, would likely have dropped in any event since Saudi Arabia typically implements cut backs that are consonant with the winter months in North America and Europe.

The U.S. lifted its 40-year ban on exporting crude oil in January which continues to affect the market and the spread between Brent and WTI began to narrow some nine months ago. The persistent problem has been over-supply, with non-OPEC suppliers being significant contributors. The green light may still be flashing for Russia and U.S. frackers to flood the market. If oil prices spiked during a production cut by low-cost producers, that would provide an incentive to open the taps wider.

The New York Fed's Oil Dynamics Report stated on Tuesday that "[o]verall, since the end of Q2 2014, both lower global demand expectations and looser supply have held oil prices down—a trend that has been reversed since the end of 2Q 2016."