Relationships like this vary over time and require firms to learn how to work together in entirely new ways. In the early 1990s, in a groundbreaking five-year outsourcing agreement with BP, Accenture (then called Andersen Consulting) took over responsibility for running the day-to-day operation of BP's accounting systems. BP retained control of accounting policy and the interpretation of data for business decision-making. In return, Accenture guaranteed BP that it would reduce the cost of running the service by 20%.