It is impossible for anyone here to predict whether you would be a competitive candidate based on the information which you have provided, because GCSE grades are only one factor, and quite often a relatively minor factor, in the process by which Oxford tutors assess candidates for admission. Your grades do not say "obvious yes" (there is no such thing - people with a bazillion 9s apply and are rejected). Your grades do not say "obvious no".
In broad terms, you will need to be on target for or have achieved A level grades of AAA (or the IB equivalent), in three rigorous academic subjects (maybe but optionally adding Further Maths IF you seek to read physics, maths, or engineering).
You will need a well written personal statement which explains your commitment to the subject that you seek to study, and mentions any super-curricular work you have undertaken (Oxford is not interested in candidates' extra-curricular activities).
You will need a glowing reference from a teacher which identifies you as academically outstanding, and explains any circumstances which impacted your GCSE grades.
You will need to do well in any relevant subject-specific aptitude test.
If invited to interview, you will need to perform well under quite high pressure.
In summary, you will need to persuade a group of Oxford academics that you have the potential to do well within the Oxford tutorial system.
You will need to be lucky - many more people apply to Oxford than can be admitted, and some good candidates are rejected. Those candidates usually go to other good universities.
Talk to your teachers. Work hard, don't burn yourself out, good luck!
Miss S Byng MA (Oxon)