An alternative look at the monthly data on banks' assets and liabilities published by APRA suggests that Commonwealth Bank is marching away from its rivals in key growth metrics.Westpac is the one bank staying in touch with CBA, and recent trends in bank balance sheets reinforce how Westpac needs to mount a takeover of St George to match the growth of its more effective rival.In consumer banking, CBA is clearly the success story in banking in the context of the credit crunch. Rather than the big banks sharing the spoils of the market share gains (in mortgages in particular) the bulk of the gains are flowing to CBA.This month the newsletter has analysed the market share of growth in home lending data over the last 12 months (rather than more subtle shifts in growth in outstanding balances) to produce a proxy for market share of new lending, or a flow measure for once.At a system level, banks in recent months continue to claim 100 per cent market share of new home lending (at least on a net basis), consistent with the pattern since the credit crunch hit.Reserve Bank of Australia credit aggregates show growth of $20.7 billion in home lending over three months, while APRA data shows growth of $22.8 billion in home lending (or a loss of a net $2 billion in three months by the non-bank sector).Obviously these are favourable times for banks in the mortgage market, but the performance of each bank is more varied than outsiders may think.Over only three months, the five largest Australian banks, in aggregate, accounted for approximately 80 per cent of the value of Australian mortgages written by banks.Their market share of the system for the top five when lending hit the crunch was more like 70 per cent, so this is obviously an improvement.But in some ways it's a surprise the top five share on a flow basis is not higher.After all, several "bank" lenders were dependent on securitisation, and the home loans books of Adelaide Bank (still reported separately by APRA) and Macquarie Bank are now shrinking, while Members Equity Bank reported only marginal growth.Among the larger banks only two are doing well in the mortgage market.Commonwealth has written a quarter of the value of Australian mortgages over the last three months.When combined with St George Bank, Westpac could claim a market share of 27 per cent, but only 18 per cent in its own right, which is only a little better than its historic market share.