What is the difference between signing up to a “reasonable endeavours” obligation on the contract, and promising to make “best endeavours”? This article from Estates Gazette makes it clear.
To summarise, promising to use “reasonable endeavours” to do something means that you should try, but do not have to exhaust all possible ways of achieving the objective, or try so hard that it compromises your own commercial position i.e. loses you money. However, if you promise to use “best endeavours” then you have to try very hard to achieve it, even if it means that it costs you.
The intermediate position of signing up to “all reasonable endeavours” probably means that you have to try various ways of achieving the objective (not just one), but not to the extent that it costs you.
There is therefore an important aspect to committing to “best endeavours” – that you may well be expected to try so hard that it incurs you in costs – that it is important not to overlook in the negotiations. If you are being asked to provide a “best endeavours” rather than “reasonable endeavours” commitment, you may want to agree to it subject to any costs that you incur being underwritten by the other side. Equally, there is value in persuading the other party in a negotiation to commit to “best endeavours” rather than the less onerous types of promise.
You can read the article here: Endeavours Obligations