The move marked AIG’s biggest rise since the news earlier this month that the company was considering the spinoff of its Asian life insurance business, AIA.

AIG jumped $1.88 to $38.65 after earlier trading above $39. The move comes some two weeks before the New York-based company is due to post its second-quarter earnings.

“That’s a little unusual to see them move that much more than the financial group,” said Randy Frederick, director of trading and derivatives for Charles Schwab. The KBW index of regional bank stocks was up 1.8%.

Frederick said options trading in AIG was heavily bullish, with just 36 puts trading for every 100 calls. A put confers the right though not the obligation to sell a stock at a certain price within a certain period, a call the right to buy.

The options action is “heavily one-sided,” Frederick said. This could be another bullish signal, though Frederick added that options trading often reacts to a stock price change rather than leading it.

So what is driving Monday’s gain? Unless there are diabolical insiders trading on an announcement to be made after the close, we may never know.

At a time of thin summer trading and little major news, “there is going to be a lot of bumping around in the market,” said Wasif Latif, vice president of equity investments at USAA. “Low volumes right now mean it can take less to move a stock.”