Bengaluru, Nov 7 (UNI) Three public sector oil marketing companies have challenged the Karnataka government's findings of 26-31 per cent ethanol in petrol at certain retail outlets, claiming that the testing methodology was not in conformity with prescribed standards and demanding independent verification of the samples. In a significant counter to the State government's findings, Indian Oil Corporation Limited (IOCL), Bharat Petroleum Corporation Limited (BPCL) and Hindustan Petroleum Corporation Limited (HPCL) said all 56 E20 petrol samples tested across Karnataka under a nationwide quality-monitoring exercise contained ethanol within the prescribed 19-21 per cent range, with the State's average recorded at…