China's top oil refiner Sinopec announced on Friday that 25 companies have paid to buy stakes in the energy giant as part of an effort to diversify state company ownership.

The completion of stake subscription is a concrete step toward a final mix-ownership of Sinopec's lucrative oil sales arm.

Friday's announcement showed the 25 partners have paid 105.04 billion yuan (17.1 billion US dollars) of 107.09 billion yuan agreed in a previous deal to Sinopec's sales subsidiary.

One of the investors failed to fully pay due to a lack of sufficient capital.

Sinopec did not reveal further details and promised to publish any progress in the cooperation in a timely manner. The company was not available for immediate comment.

Sinopec unveiled a plan last September to sell 29.99 percent of its sales arm for 107.09 billion yuan to 25 domestic and overseas companies

Among those were 11 private companies that were supposed to put in a total of 38.29 billion yuan, accounting for 35.8 percent of the new investment, according to the plan.

As China's first state company to pioneer a mixed-ownership reform, Sinopec announced last February they would solicit private capital as encouraged by the government in a bid to reshuffle and reinvigorate state-owned assets.