Saving banks is an inglorious pursuit. Lose money, and everyone is baying for your blood; turn a fat profit, and risk a political or regulatory backlash. Thus Lone Star has yet to extricate itself from Korea Exchange Bank, a deal on which it once stood to garner $5bn in profit. Now is the turn of TPG, another US private equity firm, which paid $150m for a controlling stake in Shenzhen Development Bank five years ago.

At first blush, the deal looks like a dream. TPG has agreed to sell its 17 per cent stake in the lender, based in the one-time boomtown of Shenzhen, for either cash or shares in the buyer, Ping An Insurance. The cash deal is priced at $1.68bn; a share swap, at the agreed ratio of one Ping An share for 1.74 SDB shares, is worth $2.2bn based on Monday's close. Add in dividends, and that represents a tidy return on the original investment of $660m (including subsequent take-up of share issues). Nonetheless, it is less than par for the course in China. Over the same period funds decanted into the Shenzhen bourse, where SDB is listed, would have yielded roughly one-third higher total returns, according to Bloomberg.

Besides, that is not yet money in hand. Regulatory approvals are required, and only by cashing out completely can TPG claim a clean exit. Swapping into Ping An shares leaves it indirectly exposed to SDB, still one of China's most thinly capitalized listed banks. It also becomes a shareholder in an insurer whose track record is somewhat blemished; Ping An's investment in Europe's Fortis ripped a hole in profits last year. Alas for TPG, Beijing's growing impatience with western investors selling out of its banks, and wariness about big profit headlines, suggest a share swap is the most likely option.