Use correct, not American spelling.

crypto/bio/bss_bio.c

@@ -387,7 +387,7 @@ static size_t bio_nwrite0(BIO *bio, char **buf)
 		write_offset -= b->size;
 	if (write_offset + num > b->size)
 		/* no ring buffer wrap-around for non-copying interface
-		 * (to fulfill the promise by BIO_ctrl_get_write_guarantee,
+		 * (to fulfil the promise by BIO_ctrl_get_write_guarantee,
 		 * BIO_nwrite may have to be called twice) */
 		num = b->size - write_offset;
 

ssl/ssltest.c

@@ -503,7 +503,7 @@ int doit_biopair(SSL *s_ssl, SSL *c_ssl, long count)
 		 * Useful functions for querying the state of BIO pair endpoints:
 		 *
 		 * BIO_ctrl_pending(bio)              number of bytes we can read now
-		 * BIO_ctrl_get_read_request(bio)     number of bytes needed to fulfill
+		 * BIO_ctrl_get_read_request(bio)     number of bytes needed to fulfil
 		 *                                      other side's read attempt
 		 * BIO_ctrl_get_write_guarantee(bio)   number of bytes we can write now
 		 *