HONG Kong's Hang Seng Bank and China's Bank of Communications are respectively the world's third and fourth most profitable banks, according to the yearly banking survey conducted by the UK-based international credit-rating agency, IBCA. The Hongkong and Shanghai Banking Corporation ranks at 16, leaping from 270th in 1991. The rest of the top 20 comprises 11 US banks, two Mexican banks, two Spanish banks, one Thai bank and one Singaporean bank. IBCA assesses real banking profitability each year of the world's 300 largest banks in terms of assets. The ranking, which is largely based on 1992 results, is reached after adjusting for differences in accounting, inflation and taxation. The survey reveals that size is no guarantee of success. ''Only one of the 20 most profitable banks in the world (Hongkong and Shanghai Bank) is in the list of the top 50 largest banks, ranked by assets,'' the agency says. Seven of the world's 20 most profitable banks are among the smallest 100 in the survey, that is, they fall between 200th and 300th by assets. The survey also shows some reversals of fortunes at the world's banks in the last few years. Banks in many countries continue to struggle with recession, market contraction, over-capacity, competition and even a banking system crisis, prompting state intervention, whereas others are enjoying juicy profits. ''When the aggregate performance of all banks surveyed in individual countries is taken into account, it is clear that banks in the US, Hong Kong, Thailand, China, Mexico and Spain have recently had very good years,'' the survey report says. In contrast, banking crises prevailed in the Nordic countries in 1991 and 1992. The 20 least profitable banks included 11 Nordic banks, two from the UK, two from Australia and two from Italy. Another observation made in the survey is that the top 50 banks in the world account for 53 per cent of the assets of the top 300. ''Europe-based banks account for 46 per cent of the assets (held by) the top 300, with Asia holding 40 per cent and banks from the Americas holding less than 13 per cent.''