Block-matching motion estimation plays an important role in video coding and faster, more robust and more effective search algorithms are needed. Recently, a great number of fast block matching algorithms (BMAs) have been proposed in the literature based on the discovery of the center-biased characteristics of motion-vector distribution. In this paper, a novel oriented adaptive cross search (OACS) algorithm is proposed, where small cross, large cross and T-shape search patterns are defined and utilized adaptively. In accordance with the adaptive tracing of orientation change or optimal point, three kinds of key points are defined to decide which kind or which oriented pattern may be chosen for the next step. Experimental results on the benchmarks have shown that the OACS algorithm can provide average speed ups of 74.65%, 39.78%, 42.44%, and 7.84% over DS, SDS, CDS, and SCDS, respectively. Finally, the mean absolute distortion and PSNR of luminance component are close to the results of other fast BMAs and the similar search accuracy can be maintained as expected.