July 30 (Reuters) - U.S. stock index futures extended gains slightly on Thursday, as investors assessed a barrage of economic data including a June inflation reading and the second quarter GDP estimates.

A Commerce Department report showed the Personal Consumption Expenditures (PCE) Price index fell 0.1% in June, compared with a 0.1% decrease expected by economists polled by Reuters. Annually, it stood at 3.7%, compared to estimates of 3.7%.

The core reading increased 0.1% on a monthly basis versus expectations of a 0.2% increase. It stood at 3.3% on a year-on-year basis against expectations of 3.3%.

A separate reading of advance gross domestic product showed the U.S. economy grew by 1.5% in second quarter, against estimates of 2.1% growth.

A jobless claims report for the week ended July 25 showed claims stood 197,000, compared to estimates of 200,000.

At 08:31 a.m. ET, Dow E-minis were up 231 points, or 0.45%, S&P 500 E-minis were up 48.25 points, or 0.66% and Nasdaq 100 E-minis were up 404 points, or 1.48%.