Even as global stocks lurch toward a bear market, officers and directors at U.S. companies — especially at banks — are buying.

A third of the 37 S&P 500 companies whose executives have bought their own shares in the past month are in the financial industry. Citigroup Chairman Michael O'Neill purchased about $1 million of shares on Jan. 22. as the stock plunged 18% in January. Howell D McCullough III, chief financial officer at Huntington Bancshares, on Feb. 1 snapped up 25,000 shares after the Ohio lender tumbled 22% for the worst month since 2009.

Executive buying has been higher than it is now twice since 2008 and both times proved prescient. Purchases spiked up in August 2011, just two months before the S&P 500 ended a 19% plunge. The other climax was one year after the start of the last bear market. The buy/sell ratio surged above 2.5 from below 1 in two months through November 2008 and stayed higher till March 2009, the month that marked the bottom of the worst slump in seven decades.

Insiders tend to have a longer investment horizon than most investors and when they see bargains, they can afford the risk of short-term volatility, according to Crit Thomas, a senior investment strategist at Touchstone Investments in Cincinnati, where the firm oversees $15 billion.

"Strategists often get boxed into what's going to happen over the next year," Thomas said. "If you are executives, your time frame is more lifetime based. If you see prices come down, you're going to take advantage of that. If they come down further, you can still go out and buy more. Should investors follow that? If your time horizon is more in line with the management, then maybe it's a good signal."

A total of 699 officers and directors of American companies purchased their own stock in the last 30 days compared with 828 who sold, the most bullish ratio in more than four years, according to data compiled by The Washington Service and Bloomberg. Stocks with the worst losses, such as financial firms, are seeing the biggest increase in demand.

Executives are stepping up purchases as the decline that erased more than $2 trillion in equities sends the Standard & Poor's 500 Index to its cheapest valuations in two years. Their optimism stands in contrast with Wall Street's professional equity forecasters, who have started telling clients to sell rallies.

"The purchases are a real demonstration of insiders' confidence," said Michael Arone, the Boston-based chief investment strategist at State Street Global Advisors' U.S. intermediary business. The firm oversees $2 trillion. "For the broad market direction, I'd be less confident that this is a signal that the volatility has ended. However, for the companies where insiders are buying, that's a strong signal."

The S&P 500 climbed 1% to 1,870.03 at 10 a.m. in New York, ending a three-day slide. The benchmark index had declined 13% since May through yesterday, the biggest retreat from a peak since a plunge of almost 20% in 2011. The MSCI All-Country World Index sits about 19 percent from last year's high. Jeremy Hale, head of macro strategy at Citigroup, last week advised investors to sell any rallies as further declines could open the door for the S&P 500 to go as low as 1,740.

To Mislav Matejka, JPMorgan Chase & Co.'s global equity strategist, stocks won't make a sustained recovery until the economy improves. And there are signs that weakness in manufacturing has spread to services and widening credit spreads have prompted banks to curb lending, he said.

"We remain of the view that the key strategy is to reduce equity exposure into strength, rather than using dips to buy," Matejka wrote in a Feb. 8 note to clients. "The regime has fundamentally changed."

Insiders nevertheless see bargains. At Tuesday's close, the S&P 500 was valued at 15.4 times forecast earnings, the lowest level since February 2014, data compiled by Bloomberg show. Financial shares, down 15% this year, are the cheapest among 10 main industries, trading at a P/E ratio of 11.8 and a price-to-book value of 1.15.

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