Although carbon-offsetting has gathered momentum as a way for companies to reduce their environmental impact, the best way to cut emissions is still to use less energy. And with oil trading at above $100 a barrel and energy bills continuing to rise, being more efficient makes financial as well as environmental sense. But many companies have yet to change fundamentally the way they operate in order to embrace energy efficiency. Large, high profile companies - such as UK supermarket chains Marks and Spencer, Sainsbury and Tesco - have made public commitments to cut their carbon emissions through "green" energy and energy efficiency. Energy suppliers and consultants say that the big companies that have led the way are consumer businesses that want to improve their image or heavy users of energy whose bills have become prohibitive. Smaller companies have found the move towards energy efficiency more difficult, as they often lack the resources and skills to change how they work. Npower, the UK arm of the German energy giant RWE, has been working with its business customers for several years on ways to avoid wasting energy. A survey of 200 of the company's business customers published this year showed that 77 per cent said they had taken steps to improve energy efficiency. David Lewis of Npower says that many companies have made the obvious changes, such as turning lights and computers off at the end of the day. Greater public awareness of climate change concerns and of rising energy bills means that employees are happy to co-operate, he says, and companies are prepared to criticise staff for being lax. Npower has been working with Sainsburys since 2002, when it pledged to cut carbon emissions by 10 per cent compared to 1997 levels by 2005. One of the biggest changes was to adjust the supermarket chain's power supply to a more efficient voltage. But Mr Lewis says there were also smaller alterations to Sainsburys' many lights, refrigerators and ovens that, replicated over more than 450 supermarkets, added up to a large energy saving. The company found that it could meet its emissions target solely from energy efficiency improvements. Water companies are another group that have been looking at energy efficiency. Water is heavy and takes lots of energy to move around.Last year, UK water and sewerage company United Utilities estimated that its electricity consumption had nearly doubled since privatisation in 1989. The company estimated that in 2006 it was responsible for 488,000 tonnes of CO 2 equivalent emissions and used 0.33 per cent of the electricity generated in the UK to power its water and sewage treatment plants. To tackle its rising costs and carbon footprint, United Utilities said last year that it would spend