We have studied the current induced magnetization switching (CIMS) in cobalt-based spin valve structures. Two exchange bias spin valves with extended fixed ferromagnets adopted as a current lead have been chosen for the study. The difference between them is that in the first structure, labeled EBSV (Exchange-Biased Spin Valve), no nano-oxide layer (NOL) was applied, while in the second structure, named NOL-EBSV, a NOL is inserted into the exchange biased pinned ferromagnet lead. The CIMSs in these two structures and in a non-exchange biased one, called SSV serving as the reference sample, have been studied. The temperature and field dependence of switching current in EBSV and SSV are also investigated for a better understanding the effect of exchange pinning field on the CIMS. The experiment result of CIMS in the EBSV shows a significant reduction in switching current density by a factor of 4.8, compared with a non-exchange biased spin valve with similar layer thicknesses. A double large reduction of switching current density is observed in the NOL-EBSV. We qualitatively analyze the effect of the exchange bias pinning field as well as of the nano-oxide layer on the reduction of switching current. A quantitative interpretation of the enhancement of CIMS by nano-oxide layer has been done by a three dimensional calculation of spin transport in EBSV and NOL-EBSV.