A parametric logical relation between the phrases of an Algol-like language 
is presented.  Its definition involves the structural operational semantics 
of the language, but was inspired by recent denotationally-based work of 
O'Hearn and Reynolds on translating Algol into a predicatively polymorphic 
linear lambda calculus.  The logical relation yields an applicative 
characterisation of contextual equivalence for the language and provides a 
useful (and complete) method for proving equivalences.  Its utility is 
illustrated by giving simple and direct proofs of some contextual 
equivalences, including an interesting equivalence due to O'Hearn which 
hinges upon the undefinability of `snapback' operations (and which goes 
beyond the standard suite of `Meyer-Sieber' examples).  Whilst some of the 
mathematical intricacies of denotational semantics are avoided, the hard 
work in this operational approach lies in establishing the `fundamental 
property' for the logical relation---the proof of which makes use of a 
compactness property of fixpoint recursion with respect to evaluation of 
phrases.  But once this property has been established, the logical relation 
provides a verification method with an attractively low mathematical 
overhead.