A rival bid for St George Bank or an increased Westpac offer remains probable, if the pricing of each bank's shares in the market is any guide.Shares in St George are nineteen per cent below their $38 peak just six months ago, before any specific takeover was mooted.The St George share price has historically traded with a takeover premium, but the current price earnings ratio of 15.6 is lower than the average P/E for May in the preceding four years, adding fuel to suggestions the Westpac bid is too cheap.When Westpac announced the bid for St George on Monday May 12, Westpac was trading on a P/E multiple of 12.0, with St George trading at 12.8 times and Commonwealth - Australia's largest bank - at 12.3 times.The takeover premium in the St George share price had slowly evaporated in the four months to March 2008, when the share price almost halved to $21.40, leaving St George exposed to closer scrutiny from merger and acquisition teams at the big four.This was not an option only twelve months earlier when the St George P/E multiple was 17.3 - the average P/E for the month of May 2007.By comparison, the average P/E multiple in the St George share price in May in each of the last four years was 16.2 times in 2006, 15.7 times in 2005 and 16.6 times in 2004.St George shares closed Friday at $32.32 - a twenty-one per cent gain since the bid, while Westpac shares continued to slide to $22.51 - 14 per cent lower over the same period.The Westpac offer values St George at under $30 a share, with the market anticipating a higher bid for the latter by pricing the bank at a ten per cent premium.The boards of Westpac and St George are expected to sign off on a merger agreement today or tomorrow. The two week period of due diligence agreed earlier this month runs out tomorrow.