BentMikey said:
a) it's not "stretch". Chains don't stretch, the links wear.

my experience with WD40 is quite different - chains last just as long with WD40. And I'm far from the only one.
Quite right...its just stretch is the commonly used name for its effects on a chain.
FF is also right, its ironic that one man can exert relatively little force on a chain and wear it out quite quickly, compared to the stresses and strain say an engine or conveyor chain goes through.
Ultimately, its because cycle chain is generally poor or minimalistic in quality , engineered
just well enough to do the job safely and effectively.
If WD works for you BM, who am i to argue. My experience has been different, but hey ho
As stated by another poster, oiling a chain is with different products is a lottery IME.
Ive tried WD, didnt work well for me.
Ive tried engine oil, very regular removal of chain, clean and soak in a bath of oil then refit.
Ive tried Finish Line Dry (IIRC) ...the chain gets just as dirty, but i havnt noticed any extra life from the chain.
I use Rocol Sapphire Precision Lube (actually quite expensive)...again i cant say ive seen any extra life in the chain.
I come to the conclusion, cycle chain (9 and 10 speed) is poor quality (or unable to resist wear to put it kindly) and doesnt last whatever you do.
Use whatever you like...its never made any difference to mine