The falls came after both benchmarks recovered around 12 percent from their recent lows on June 21.
Many traders closed positions ahead of the U.S. Independence Day holiday on July 4, while Brent also faced technical resistance as it approached $50 per barrel, traders said.
Despite this, market sentiment has shifted somewhat.
Late May and most of June were overwhelmingly bearish as U.S. output rose and doubts grew over the ability of the Organization of the Petroleum Exporting Countries (OPEC) to hold back enough production to tighten the market.
But sentiment began to shift towards the end of June, when U.S. data showed a dip in American oil output and a slight fall in drilling for new production.
"We see a recovery for oil prices in H2 2017 from current levels, with OPEC production cuts, a slowdown in global supply growth and seasonally firming demand driving up prices," BMI Research said, although it added that "large-volume supply additions will keep price growth flat y-o-y in 2018."