This paper attempts to systematise the distribution of variant forms of the Old English prepositions by, for and between. Using evidence from the variable positioning of their object personal pronouns, I argue that by and for each have two prosodically conditioned allomorphs; one that is phonologically dependent on its object (like French de ‘of’ as in Jean a beaucoup d'argent ‘John has lots of money’) and another that is not. Patterns in the distribution of variant forms of between have previously been noted but remain partially unexplained. I offer a novel analysis of the tendency for personal pronouns to occur to the left rather than the right of betweonum and of the tendency to use that particular variant of between when its complement is a personal pronoun.