… terms, the agreement upon which is regarded by the parties themselves as an essential prerequisite of the making contract. These are terms which parties expressly agree to settle before any agreement becomes legally binding and which usually shortened to SUBS.
Per Legatt J in The Nissos Samos  1 Lloyd’s Rep 378 at 385:
‘Subject details’ is a well-known expression in broking practice which is intended to entitle either party to resile from the contract if in good faith either party is not satisfied with any of the derails as discussed between them.
By Steyn J in The Junior K  2 Lloyd’s rep 583:
It is plain that the parties had in mind a contract on the Gencon form but that they not yet considered the details of it. By the expression subject to details of the Gencon charterparty the owners made clear that they did not wish to commit themselves contractually until negotiations had taken place about the details of the charterparty. Such discussions might have covered a number of clauses. It does not follow that the owners were willing to accept all the detailed provisions of the standard from document. After all, this a common occurrence for some of the detailed provisions of the Gencon form to be amended during the process of negotiation. In any event, the Gencon standard form contains within it alternative provision which require a positive selection of the desired alternative.
…it seems to me clear that the stipulation ‘subject to details of the Gencon charterparty’ conveys that the fixture is conditional upon agreement being reached on the details of the Gencon form, which had not yet been discussed.