Mr Gilmore had been scheduled to finish his tenure at the end of next year.

According to sources, Mr Gilmore left Hong Kong yesterday, and was returning to his native United States.

A replacement for Mr Gilmore may not be necessary due to the planned merger of the stock exchange and futures exchange and their clearing houses next year.

The merged entity is to have only one chief executive.

Mr Gilmore's departure further undermines the exchange's plan to shift Hang Seng Index futures and options to an electronic trading system from the open outcry standard.

The exchange missed its August 2 deadline for the move and is unable to schedule a start date because of its troubled Hong Kong Automated Trading System (HKATS).

The system has failed six simulated trading tests.

Yesterday, futures exchange chairman Geoffrey Yeh Meou-tsen said work would continue towards 'the successful migration of the Hang Seng Index futures and options to electronic trading'.

Market sources have speculated that any electronic trading of HSI futures on the HKATS will probably be delayed until next year, to allow more time for testing.

They also said the futures exchange might scrap the system.

The stock exchange's proposed new trading system - the third generation of the Automatic Order Matching and Execution System (AMS/3), could be a possible choice for the futures exchange, the sources said.

Such a move could be in line with government expectations.

Last month, the Government released a paper introducing the exchange that would be created by the merger of the stock and futures markets.

In the paper, the Government indicated the exchange would provide 'a unified trading platform' for the stock and futures markets to increase trading efficiency.

A stock exchange spokesman said yesterday AMS/3 could handle futures trading.

A Government source said there was no assurance of this, as the AMS/3 would not be launched until next year.

Sources said Mr Gilmore was forced to resign due to the delay in the migration plan for the futures exchange and the lack of transparency in the HKATS.

Furthermore, Mr Gilmore allegedly misled the public about test results.

According to a market rumour, he presented results to the Securities and Futures Commission that differed from figures released to the public.

However, an SFC spokesman would not confirm the rumour.

She also would not comment on whether the commission had pressed Mr Gilmore to step down.

Mr Gilmore said in a statement yesterday that his resignation 'was due to personal reasons', and did not elaborate further.

The futures exchange did not disclose the terms of Mr Gilmore's departure.

His resignation made it unlikely he would receive compensation or a bonus from the exchange, sources said.