CITIGROUP'S $7.5 BILLION SALE OF CONVERTIBLE bonds last month to the Abu Dhabi Investment Authority, a deal that helped the bank boost its finances amid credit market turmoil, highlights the rising popularity of convertibles. The first nine months of 2007 saw $67 billion issued, up 46 percent from the same period last year, according to Dealogic. For the 12 months ended November 14, banks earned $2.98 billion in fees from convertibles deals, up 38 percent from the prior 12 months. Convertibles are bonds that become stock if the issuers share price reaches a preset level. For investors theyre a conservative way to bet on stocks rising; for issuers they offer lower interest costs than straight bonds. That makes convertibles popular toward the end of stock rallies and amid rising debt capital costs much like todays prevailing market conditions. The charts above show which firms are getting the biggest shares of the surge in convertibles fees.