(Yicai Global) May 15 -- Two leading Chinese banks and the country's biggest oil producer are among the 234 mainland stocks that MSCI Inc. will add to its Emerging Markets Index and others at the start of next month, marking a pivotal moment for the opening up of the country's stock markets.

The nation's biggest and second-biggest banks, Industrial and Commercial Bank of China Ltd. and China Construction Bank Corp., both state-owned, will join the index, MSCI said in a statement today. PetroChina Co. will join them to form the three heaviest Chinese additions to the benchmark.

The stocks will be added at 2.5 percent of their Foreign Inclusion Factor-adjusted market capitalization, the statement added, giving them aggregate weights of 1.26 percent in the China Index and 0.39 percent in the Emerging Markets Index. The move will mark the first step of Chinese stock inclusions, with the second phase increasing the FIF-adjusted market cap to 5 percent and coinciding with the August 2018 quarterly index review.

MSCI decided to include Chinese stocks in the Emerging Markets Index last June, marking a critical step forward for the opening of the country's capital market and giving international investors better access to its shares. Swiss bank UBS Group AG expects the additions will bring about USD18.5 billion into mainland stocks during the first phase, with more money pouring in after the August adjustment.

MSCI launched the Emerging Markets Index in 1988 and the benchmark now tracks 24 countries representing 10 percent of world market capitalization.

Editors: Emmi Laine, James Boynton