Mumbai, Aug 3 - A key index of the Indian equities markets opened marginally in the green Monday and was ruling 21 points up about five minutes into trade.

The sensitive index (Sensex) of the Bombay Stock Exchange (BSE) opened at 15,694.78 points, as against Friday's close at 15,670.31 points. It then slipped mariginally to 15,691.74 points, still 21.43 points or 0.14 percent up.

The broader S&P CNX Nifty of the National Stock Exchange (NSE) was also ruling in the positive terrain at 4,637.7 points, though it was a gain of a meagre 0.03 percent.

Broader market indices were also in the green, with the BSE midcap index trading 0.32 percent higher, and the BSE smallcap index up 0.35 percent.