Contracts often use certain phrases when each party agrees in principle to do things to fulfil an obligation but neither party has the time, money or inclination to drill down into exactly what each party is expected to do.
Typically used phrases include, that parties will use their, “best endeavours”, “best efforts”, “all reasonable endeavours” or “reasonable endeavours”.
Quite what these phrases really mean, legally, has always been a grey area. This issue has been brought into focus by a recent High Court case* where one party successfully sued another because it did not use, “all reasonable endeavours” to sign an agreement.
What that High Court judgment makes clear is that using these phrases in a contract imposes a clear and binding legal obligation – the scope of which will be determined by the words and context of each case. For example, if you promise to use your “best endeavours” to achieve something, then complete passivity is likely to be a breach. Depending on your situation, you may even need to incur some cost or inconvenience to fulfil a “best endeavours” obligation. Rather than promising to use your “best efforts”, it would be better to list the tasks that need to be done or it may be even more important to include details of what you are not willing to.
*Brook Homes (Bicester) Ltd v Portfolio Property Partners Ltd  EWHC 3015 (Ch)