The opposition applies to the European patent in all the contracting states in which that patent has effect. Thus the opposition has, in principle, to be in respect of all the designated states. If an opposition is filed in respect of only some of the designated states it will be treated as if it were in respect of all the designated states.[Art. 99(2); ]

Nevertheless, the effect of an opposition may differ as between contracting states. This may arise where the patent contains different claims for different contracting states in accordance with Rule 18(2) (see C‑IX, 2.4), or where the claims must take account of different art under the provisions of Art. 54(3) EPC 1973 and of Art. 54(4) EPC 1973 (see D‑VII, 8). Amendments may also be occasioned by national rights of earlier date within the meaning of Art. 139(2) and Art. 140 (see H‑II, 3.3, and H‑III, 4.4). Thus the patent may be differently amended in respect of different contracting states and may be revoked in respect of one or more contracting states and not in respect of others.[Art. 61; Art. 139(2); Art. 140; ]