Aug 12 (Reuters) - U.S. stock index futures pared gains slightly on Wednesday as investors assessed a largely in-line inflation reading for July.

A Labor Department report showed the Consumer Price Index rose 3.4% on an annual basis in July, in line with an estimated 3.4% rise, according to economists polled by Reuters. On a monthly basis, it rose 0.1% compared with an expectation of a 0.1% rise.

Excluding volatile food and energy components, core CPI increased 2.5% annually in July, versus an estimated 2.5% gain. It stood at 0.2% on a monthly basis, versus an expectation of 0.2%.

At 08:32 a.m. ET, Dow E-minis were up 134 points, or 0.25%, S&P 500 E-minis were up 28.75 points, or 0.37%, and Nasdaq 100 E-minis were up 249.75 points, or 0.84%.