Every year, Two Tomorrows releases the Tomorrows Value Rating of the Oil and Gas sector --an assessment of the corporate responsibility practices of the largest oil and gas companies in the world. Last week marked the 2010 release with BP leading the Rating with a score of 59 out of a possible 100 points. There are inevitably, and justifiably, questions that result from a rating of this nature.

For example, what does a score of 59 percent mean? Does that mean that, in our opinion, BP is "more than halfway to being sustainable"? Aren't oil companies -- which extract non-renewable resources to produce a product that inevitably contributes to climate change -- inherently fundamentally unsustainable? If that's the case, how can a rating methodology hope to measure the "responsibility" of an oil company?

Let's first tackle the philosophical implications of an oil and gas, corporate responsibility rating. One thing is certain: The extraction and combustion of fossil fuels is not sustainable. It's not clear which will give out first, oil reserves or our capacity to endure the impacts of climate change, but regardless of the order, the current energy model is not sustainable.

Further, while the International Energy Agency continues to say that fossil fuels will remain the dominant source of energy for the next two decades, given the world's growing energy demands -- especially in emerging economies -- demand could potentially outstrip supply sooner than anyone would like to see.

This does not mean that an oil company itself is unsustainable; in fact it has the capacity to innovate and evolve. Therefore any assessment of corporate sustainability must evaluate the capacity and commitment of the oil company to innovate and lead toward the next energy model.

Innovating and developing the energy future is a clear responsibility for the oil and gas sector. Of equal importance to society is the responsibility to deliver today's energy. It would be a truly irresponsible oil company that did not work to guarantee secure energy supplies. Economic growth and social development depend on access to energy. Turning off the oil supply today is no more an option than business as usual.

Add to this fundamental dilemma the fact that responsible (and sustainable) oil companies must also balance the needs and priorities of a wide range of stakeholders. From employees and shareholders to customers and communities, responsible oil companies must address issues ranging from environmental protection to job security and from protection of human rights to local economic development.

It is far too simple to suggest that oil and gas companies are agents of social and environmental destruction given the array of impacts (both good and bad) that they have on today's world. An assessment of sustainability and corporate responsibility in the oil and gas sector must, therefore, take a measured approach.

On the one hand, the assessment cannot turn a blind eye to the inherently unsustainable practice of using a non-renewable resource to fuel global development and then suggest that the companies undertaking this approach are "sustainable." On the other hand, the assessment must acknowledge that the oil and gas sector has a wide range of impacts and responsibilities.

It is important that an assessment of sustainability be based on what the company does, not what it says, while at the same time not being biased toward high-profile incidents of good or poor practice. And most importantly, the assessment should measure the ability of the company to move away from the current energy model into a more sustainable energy future while balancing and protecting the priorities of all of its stakeholders.