(104)The obligation to deliver the best possible result when executing client orders applies in relation to all types of financial instruments. However, given the differences in market structures or the structure of financial instruments, it may be difficult to identify and apply a uniform standard of and procedure for best execution that would be valid and effective for all classes of instrument. Best execution obligations should therefore be applied in a manner that takes into account the different circumstances associated with the execution of orders related to particular types of financial instruments. For example, transactions involving a customised OTC financial instrument that involve a unique contractual relationship tailored to the circumstances of the client and the investment firm may not be comparable for best execution purposes with transactions involving shares traded on centralised execution venues. As best execution obligations apply to all financial instruments, irrespective of whether they are traded on trading venues or OTC, investment firms should gather relevant market data in order to check whether the OTC price offered for a client is fair and delivers on best execution obligation.