Saudi Aramco's shares opened lower at SAR37.50 on the Saudi Stock Exchange (Tadawul) following its inclusion in the MSCI, Tadawul indices.
The stock was down 1.6% at SAR37.20 in early trading on Wednesday.
Aramco's inclusion on global index provider MSCI would attract around $2.4bn in both passive and active inflows.
Both the Tadawul All Share Index (TASI) and the MSCI Index were marginally up.
Separately, Saudi Aramco said that Goldman Sachs may stabilize an offer of 3 billion of the oil giant's shares.
The investment bank was named Aramco's stabilizing manager for its initial public offering earlier this month.
A stabilizing bid is a purchase of stock by underwriters to support the price of a stock immediately after its listing.
The first stabilization period for Aramco shares will end on January 9 2020, the company said in a statement.