The SEC found numerous causes for stock run-ups.

A sharp rise in stock prices before a takeover announcement may not be linked to illegal inside trading, but instead may be due to press speculation and legitimate research, according to a Securities and Exchange Commission study. The study looked at 172 mergers and found an average 38.8% run-up in stock prices before a deal was announced. But it said much of that was due to press reports and speculation, an active and legitimate market for information and early “foothold” buying by those attempting the takeover.