The high-stakes worlds of casinos, hotels and banking are most susceptible to suspicious share trading ahead of big merger and acquisition announcements, according to analysis carried out by the Financial Times.

Abnormal share trading has been seen far more often ahead of large deals in these industries than in insurance or telecoms, suggesting they may be more vulnerable to insider trading.

The FT analysis shows that 80 per cent of hotel and casino M&A deals since 2003 saw abnormal trading in the days leading up to an announcement. The banking industry comes second with 52 per cent of deals in the same period showing suspicious share movements.

The FT examined trading data for the top 100 USand Canadian deals since 2003 collected by Measuredmarkets, a Toronto research firm that uses a weighted average based on volume, price and number of trades to flag unusual trading patterns. The survey found suspicious trading occurred ahead of 49 per cent of all North American deals.

Deals in the telecoms industry showed the lowest level of suspicious trading at 33 per cent, followed by media at 38 per cent and insurance 43 per cent.

While the suspicious moves detected by the Measuredmarkets data may indicate insider trading, the data is not proof that improper trading occurred, nor does it flag every insider trade.

Insider trading may vary from sector to sector because non-public information may yield higher returns in some industries than it does in others, says Henry Hu, a corporate and securities law professor at the University of Texas.

The variation by sector may also be due to hedge funds preferring certain types of stocks over others, said John Coffee, a Columbia University law professor. Mr Coffee, who has testified on hedge funds before the US congress, said some funds may be more willing than other investors to take the risk of trading on improperly obtained inside information.

Measuredmarkets does not track call or put options, which are often used in insider trading. On Friday, the US Securities and Exchange Commission filed a civil complaint against Taher Suterwalla of London, alleging he used call options purchased through a Swiss bank to trade ahead of Petco Animal Supply's announcement it would be acquired by two private equity firms. No trial date has been set.

Though Measuredmarkets flagged 49 deals for suspicious trading, only a handful have been the subject of civil or criminal cases.

Sometimes the Measuredmarkets data appears spot on. The firm flagged April 16 and 17 for deviant trading in Dow Jones shares when the prices rose 4.8 per cent. On April 30, News Corp made public its $60-a-share bid. In May, the US Securitiesand Exchange Commission charged a Hong Kong couple with insider trading, alleging they improperly purchased 415,000 Dow Jones shares between April 13 and 30.

The SEC declined to comment on the FT survey.

But Rick Ketchum, chief of regulation for the New York Stock Exchange, said: "Our surveillance systems allow us to review and investigate anomalous patterns that may constitute insider trading and market manipulation."

Additional reporting by Brooke Masters