Expro International, the UK oil and gas exploration specialist, is on the market and has received two substantial offers.Expro had received a £1.6 billion bid from Candover and Goldman Sachs, and was discussing a takeover when US-based Halliburton Group proposed a £1.7 billion offer for the business.The US engineering giant Halliburton has been running a due diligence process on Expro and has until this weekend to decide whether to submit a formal £1.8bn counter offer.