Reporting agencies should accept oversight After Libor returns from reform school as a more honest, reality-based rate, what should regulators turn to next? Anywhere you can have a "max bullshit number." That evocative phrase describes the game better than the emails revealed in the Barclays probe. It also shows that the operators exist in other markets. Paul Atha, a former natural gas trader for Mirant Corp, deserves the credit for coining it. In a recorded phone call in 2000, Atha described the biggest lie he thought he could get away with in reporting trades as the "max bullshit number" (MBN), according to a complaint by the US Commodity Futures Trading Commission, which was eventually settled. Like the Libor submitters, Atha and other traders were accused of trying to influence industry prices by reporting false trades. The main difference lies in to whom Atha was reporting. Barclays and its peers reported numbers to the British Bankers' Association, an industry trade association which for years defended the integrity of their broken process. Mr Atha reported to someone like me. Some years ago I worked for a company that publishes commodity prices. I would phone gas traders who would give me a list of trades. I would enter them in a spreadsheet that spat out a magic benchmark. Those magic numbers were not as important as Libor, with its impact on an estimated $350tn of contracts, but they still affected markets around the world. I hope that my amiable gas traders always told the truth and the full truth but I have no way of knowing. Concern over the way in which Platts, Argus and the other "price reporting agencies" operate has risen to the level of the Group of 20. Regulators are due to report to their political overlords later this year on whether - and how - the system should be reformed. The CFTC, which led the US end of the Libor investigation, is particularly uneasy about the PRAs, according to staff and public speeches by Scott O'Malia, a Republican commissioner, and Gary Gensler, the Democratic chairman. They have their eye on increased oversight. At their best, the PRAs should not have the conflicts of interest of a trade association. Though regulators are looking for potential conflicts, I've no reason to think there are any. But even when it works, the PRAs" insistence that they are engaging in journalism - with all the gilded significance the trade still has in the US - is a roadblock to regulators" hopes of reform. McGraw-Hill, owner of both Platts and Standard & Poor's, relies on the same defence for potential problems in each company: freedom of speech. No, you can't hold us responsible for our credit ratings: they're a matter of opinion. No, you can't have our spreadsheets: we're protecting our sources. If the PRAs are smart, they will drop their objection to more oversight if it strengthens their claims to integrity. The CFTC and Congress should push them. At the same time, it's important we recognise just how rarely we are ever likely to spot the MBN. Regulators cannot rely on banks reporting wrongdoing, as Barclays did, or traders being so stupid as to detail their misdeeds in email as both Barclays and Mirant's traders did. Even if benchmarks for interest rates and gas prices are decided on transparent transactions, there is still room for manipulation: for example from "wash trades" where a trader buys and sells at the same price, ending up with a neutral position but affecting an index. And as anti-banker sentiment reaches a new level of toxicity, we should remember that it's not just rates traders in New York or gas traders in Georgia who reach for the MBN. Part of the reason so few Americans are taking advantage of record low interest rates to refinance their mortgage is a scam that was probably more detrimental to global finance than attempted Libor rigging. Middle-class Americans who wanted a mortgage that their income didn't justify simply invented a MBN in their salary. This is difficult to do now. The "no-doc" loan that allowed them is a thing of the past and documentation is now maddeningly rigorous. So those with "liars" loans" cannot refinance into cheaper mortgages because they lied on their first forms and can't lie again. The manure is all around us. Tom Braithwaite is the Financial Times's US Banking Editor.