All three have joined the Championship side until the end of the season.
Oxford, 18, made his Hammers debut in the Europa League when he was just 16 and signed a new four-and-a-half-year deal with his parent club in December.
Mutch, 25, has played eight times for Palace this season while Grabban, 29, has made just six appearances.
All three players could feature for the Championship promotion hopefuls against Ipswich on Saturday.
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Reading have signed Bournemouth striker Lewis Grabban, West Ham defender Reece Oxford and Crystal Palace midfielder Jordon Mutch on loan.