Benchmark oil for December delivery was up 95 cents to 87.87 dollars (£55.26) per barrel in late afternoon Bangkok time in electronic trading on the New York Mercantile Exchange. The contract added 1.05 dollars to finish at 86.92 dollars (£54.66) per barrel on Friday.
Brent crude, used to price many international varieties of oil, rose 77 cents to 109.72 dollars (£69). It closed at 108.95 dollars (£68.53) per barrel in London on Friday.
Gordon Kwan, head of energy research at Mirae Asset Securities in Hong Kong, said some investors fear that oil supplies could be disrupted if the Israel- Hamas conflict engulfs countries elsewhere in the Middle East, a huge producer of crude.
The "market is putting a geopolitical premium on the price of oil amid escalating tensions between Israel and Palestine and that could continue for some time", he said.
The fighting comes just as winter arrives in the US and China, at time when energy demands climb.