President Trump recently said the quiet part out loud.

“We may have to fight for the oil. It’s O.K.,” he said. “Maybe somebody else wants the oil, in which case they have a hell of a fight. But there’s massive amounts of oil.” The United States, he added, should be able to take some of Syria’s oil. “What I intend to do, perhaps, is make a deal with an ExxonMobil or one of our great companies to go in there and do it properly,” he said. The goal would be to “spread out the wealth.”

At the very least this amounts to pillaging, but then respect for the law isn't on Trump agenda.

Trump is "protecting" Syria's oil in the exact same way that the mob "protects" a small businessman from arson.
Not kind of the same way. EXACTLY the same way.

Trump comment US intends to keep the oil in Syria. Guard with US armored forces. Bring in US oil companies to modernize the field. WHAT ARE WE BECOMING.... PIRATES? If ISIS is defeated we lack Congressional authority to stay. The oil belongs to Syria. https://t.co/Leko5s1hXF

— Barry R McCaffrey (@mccaffreyr3) October 28, 2019

So what "great companies" would be willing "to go in there" and “spread out the wealth?”
That company turned out to be ARAMCO.

Sources have disclosed that the Saudi Arabian Oil Company, commonly referred to as Aramco, has sent a delegation of experts to discuss investment opportunities in the oil fields and wells in the Eastern Syrian city of Deir Ez-Zor.

According to the oppositionist news site Deir Ezzor 24, Aramco “started implementing practical steps in this field, where a group of the company arrived in an official mission to al-Omar oil field in the eastern Deir Ezzor countryside.”

There is no legal means to do this. This is the outright theft of resources.
And it keeps getting worse.

It is believed that the investments will be made through contracts signed between Aramco and the US government, whose armed forces have steadily been increasing their military presence in terms of manpower and equipment around the oil fields.

That is trafficking in the sale of stolen property, but it gets even worse than that.

The Kurdish Syrian Defence Forces (formerly known as the YPG) currently control most of the country’s oil fields and have shifted towards an alliance with the Syrian government after losing American protection in the north-east of the country in the wake of Trump’s “withdrawal” and ensuing Turkish offensive dubbed “Operation Peace Spring” to clear the area of Kurdish militias

So we can't even pretend to be doing this for the benefit of the local population, our regional allies, or any other justification except naked theft.
Trump should be in jail for this.

"I think in this case we are not talking about an operation associated with a huge share of risk, but, on the contrary, about a well-thought-out operation.”
- Professor RSUH Grigory Kosach

The Pentagon is enthusiastically cooperating in this blatant violation of international law.
US troops have returned to six out of 16 bases in Syria that had been previously abandoned during the October withdrawal.
What's more, our military is settling in for the long haul.

Barely two months after US President Donald Trump’s demagogic announcement that he was pulling US troops out of northeastern Syria to fulfill his campaign promise to bring a halt to Washington’s “endless wars,” the senior civilian and uniformed Pentagon chiefs told a House panel Wednesday that there is no foreseeable end to the American presence there.
...
Esper went even further, insisting that US military forces had to remain in Syria not so much to counter any existing military force, but rather an “ideology”.

“I think the defeat, if you will, will be hard because it’s an ideology,” Esper told the House panel after repeated questions regarding US strategy in Syria. “It’s hard to foresee anytime soon we would stamp it out,” he added.

Everyone that somehow finds a way to defend Trump based on his so-called aversion to foreign wars needs to take a good, hard look at this. Because THIS is 100% Trump's doing.