如果有可比性的话，两者是都有自己、亲自的意思，但用法不同:
oneself_百度翻译
[英] [wʌnˈself][美] [wʌnˈsɛlf]
pron.
自己，自身; 亲自，自行; 其; 亲手;
[例句]
It is a very rewarding exercise to work this out oneself
独自解决这个问题是一次受益匪浅的锻炼。
同一句用后者就要
It is a very rewarding excercise to work out on his own.
要加个on
追答work this out on his own
但在of oneself时可以通用
[例句]
One must have a correct estimate of oneself/himself.
对自己要有正确的估价。
这就好比中午文里“人对（他）自己得正确评价”，加不加他都可以