The point is that a reasonable endeavours obligation may be discharged by exhausting just one of the number of possible solutions, whereas best endeavours (and ‘all reasonable endeavours’) requires all avenues to be explored. In practice, it seems that ‘all reasonable endeavours’ is treated the same as ‘best endeavours’.

Note that commercial undertakings are usually interpreted subject to a proviso that the person giving the undertaking is not expected to act in a way that is detrimental to its own ‘commercial interests’. The exact scope of this exception remains unclear. One example was P&O [1994] where L was under an obligation to use reasonable endeavours to secure lettings on a development – but because of the property collapse, this would have meant L paying reverse premiums to Ts. Accordingly, the HL decided that ‘reasonable endeavours’ did not extend that far.

One way of avoiding such problems, and achieving certainty, is to try to specify in the contract the actions a party must take in using ‘best or reasonable endeavours’; if specific actions are required then arguments about ‘commercial interests’ can no longer arise. For the authorities see [2007] 189 Property Law Journal 22.. © Practical Lawyer