A customized jet cup for measuring attrition resistance of oxygen carrier particles for chemical looping combustion has been constructed and used to evaluate 25 different material samples, all of which previously have been subject to continuous operation in chemical looping reactors at Chalmers University of Technology. The effect of continuous operation has been assessed by comparing attrition behaviour of fresh particles with that of used ones. It is concluded that the correlation between the jet cup tests and operational experience is robust, and that there is always considerable difference in attrition resistance between fresh and used particles of the same batch. Composite materials with NiO or Fe 2 O 3 as active phase and Al 2 O 3 -, NiAl 2 O 4 -or MgAl 2 O 4 -based support and materials based on the CaMnO 3-δ perovskite structure typically had high attrition resistance, which improved further following operation with fuel. Combined (Fe x Mn 1-x ) 2 O 3 oxides and all materials containing smaller or larger amounts of either CuO or ZrO 2 experienced reduced attrition resistance during operation with fuel, and usually also had low attrition resistance to begin with. Fresh particles of the commonly used oxygen carrier ilmenite had reasonably high attrition resistance, while ilmenite that had been subject to chemical looping combustion of natural gas showed higher rate of attrition. No strong correlation between the commonly used crushing strength index and attrition resistance measured with jet cup could be established, but it was clear that particles with a crushing strength above 2 N were much more likely to have high attrition resistance compared to softer particles. As compared to crushing strength, the jet cup testing were better correlated to attrition in actual operation.