This study experimentally explores the influence of support methods, surface geometry, and standoff distance on erosion due to a submerged cavitating oil jet. In examining the support effect, specimens were either rigidly supported using a solid mount or flexibly supported using alternatives such as O-rings, rubber washers, and coil springs. For the geometry effect, three protrusions were formed around the jet-impinging surface of the specimens. In terms of the distance effect, the standoff distance between the nozzle and the specimen was adjusted to near the maximum eroded distance. Specimens were prepared from an aluminum alloy with an impinging surface of 15 mm in diameter, and supported either rigidly or flexibly using various elements and jigs. VG32 hydraulic oil was used as the test liquid and the upstream pressure was set to 10.1 MPa. The experiment demonstrated that the use of O-rings reduced the mass loss of the specimens. However, standoff distance and impingement surface geometry were as much or more effective than supporting flexibility under the studied conditions.