(Adds quotation, background)
JOHANNESBURG, Jan 16 (Reuters) - South African PresidentJacob Zuma has asked parliament to reconsider a bill giving thestate a free 20 percent stake in gas and oil ventures, believingit might not survive a potential challenge that it isunconstitutional, the government said.
Parliament passed the changes to its main petroleum law lastMarch, alarming companies such as Shell, Total and Exxon Mobil, which are looking to explorein South Africa.
"After careful consideration of the Bill and the submissionsreceived, the President is of the view that the Bill as itstands would not pass constitutional muster," the Presidencysaid in a brief statement on Friday.
Zuma must assent to and sign all bills passed by parliamentbefore they become South African law.
Mineral Resources Minister Ngoako Ramatlhodi said in Julythe government might reconsider the legislation to ensure thatinvestors could make profits while securing a place for thestate in the sector..
The government has outlined ambitious plans for oil and gasexploration in coastal waters that it says could contain as muchas 9 billion barrels of crude and vast quantities of naturalgas. (Reporting by Stella Mapenzauswa; Editing by Mark Potter)