Brent crude futures for September, which expires on Friday, fell 45 cents, or 0.6%, to $75.60 a barrel, following a 1.75% jump on Thursday.
The more active Brent contract for October was down 48 cents, or 0.6% to $74.62 per barrel, Reuters reported.
US West Texas Intermediate crude futures fell 43 cents, or 0.6%, to $73.19 a barrel, whittling down a 1.7% rise from Thursday.
But both benchmark contracts were headed for gains of around 2% for the week, buoyed by indications of tight crude supplies and strong demand in the United States, the world's biggest oil consumer.
US refiners Valero Energy and PBF Energy have reported quarterly results that surpassed analysts' expectations.
Even with coronavirus cases rising in the United States, all around Asia and parts of Europe, analysts said higher vaccination rates would limit the need for the harsh lockdowns that gutted demand during the peak of the pandemic last year.
Analysts also point to a rapid rebound in India's gasoline consumption and industrial production following its Covid-19 surge earlier this year as a sign that economies are more resilient to the pandemic.