Concentration ratios are rising, albeit slowly, in the sector occupied by credit unions, building societies and the newly minted mutual banks.The annual review by KPMG of the sector shows that in 2011 the top 10 credit unions and building societies accounted for 63 per cent of total sector assets, which stood at A$83 billion.In 2006, the top 10 CUBS accounted for 57 per cent of assets.The largest credit unions may not be the most profitable. According to the KPMG survey, the top 10 accounted for 54 per cent of sector profits, of $539 million, in 2011. In 2006, the top 10 accounted for 52 per cent of profits.Over five years, the number of CUBS has declined by 49 to 113, a number that's steadily shrunk from the many hundreds of small deposit-taking institutions 20 years ago.Australian Prudential Regulation Authority data shows the CUBS sector maintained profitability over the year to June 2011, with return on assets steady at 0.7 per cent over the previous year, and the return on equity steady at 8.7 per cent.While KPMG surveys all 10 building societies, it surveys only larger half of the credit union segment, or 66 out of the 103. This group of credit unions accounts for $55 billion out of $56 billion in sector assets.The 66 credit unions made an aggregate profit of $376 million over the financial year, KPMG said. All credit unions in the KPMG survey made profits.According to APRA, aggregate credit union profit for the year was also $376 million.That leaves 37 small credit unions (with total assets of $1.4 billion) earning a combined profit of zero.