Questions of industry structure in an oligopoly sector occupied a speech on Thursday by Rod Sims, the chair of the ACCC, for a Communications Day conference.Yes, the stated topic for Sims was telecommunications, but give it a go and substitute banking.In September 2012, Sims said, "David Thodey, then CEO of Telstra, stated that 'all the data we've looked at around the world says three [operators in a market] are very rational from a pricing perspective. Once we get to four or five is when you start to get behaviour that can be aberrant in terms of shareholder value."And that, Sims said, was "all commercial common sense," as well as the prelude for mischief in more than the telco sector."In my terms, therefore, introducing a fourth mobile network operator, TPG, will be great for consumers. So will Vodafone's entry into fixed broadband."Sims continued: "In my view having four mobile and five major broadband players is to be welcomed, encouraged and, as much as possible, retained over the longer term. "Indeed, I am of the view that there is increasing room for a fourth player in the mobile network market. TPG has been a vigorous competitor in the fixed broadband market and who doubts it will be the same in the mobile world?"Now pair Sims thoughts on facets of market structure with those of Michele Bullock, assistant governor, financial system at the RBA, at the Economic and Social Outlook Conference in Melbourne on Friday."The major Australian banks are very profitable," was about the only warm comment allowed on the oligopoly in a conference session with the theme, "are the banks too big?"Bullock wound up her analysis of this question in economist's style."I want to reiterate that the concentration of the banking system in four major banks in Australia does not necessarily provide financial stability benefits. "Nor is it necessarily detrimental to financial stability. "But the systemic importance of the four major banks in Australia does mean that they need to have a proportionately greater supervisory focus. "The strengthening of capital and liquidity standards post-crisis, and the use of proactive and intensive supervision, has certainly improved the resilience of the major banks in Australia, and the financial system more broadly."The follow up to the work of the G20's and David Murray's panel for the Financial System Inquiry means "the Australian financial system is more resilient to shocks than it was in the past," Bullock said. "But there is still a need to consider what might happen in the event of a bank failure."Bullock set out the RBA's (and APRA's and others') take on the rationale for this years' innovation on macroprudential policy.The concern, she said, was that competition was manifesting itself in an erosion of lending standards. "Not only were the banks taking on more risk, but households were carrying a higher level of debt that they would have to service, which could be particularly concerning in the event of a shock. "In other words, it was a financial stability issue not only because