Background: Normalization of oesophageal acid exposure using high dose proton pump inhibitors in patients who are candidates for ablation therapy has been suggested to be essential for successful Barrett's reversal. However, the success rate for achieving pH normalization has not been determined. Methods: Patients with Barrett's oesophagus (2–6 cm in length) who were found to be eligible for ablation therapy using multipolar electrocoagulation were included in this prospective study. Patients underwent an upper endoscopy to determine Barrett's length and other anatomic characteristics. Biopsies were obtained to rule out dysplasia. Subsequently, patients were treated with omeprazole 40 mg b.d. Twenty‐four hour oesophageal pH monitoring was performed after a mean period of 8.4 ± 0.6 days of therapy. Results: Twenty‐five patients were enrolled into the study. The pH test was abnormal in four (16%) of the study subjects. An additional two (8%) patients had abnormal supine percentage time with pH less than 4. There was no significant difference in oesophageal acid control between patients with long vs. short segment Barrett's oesophagus. Elderly (> 60 years) patients tended to have less acid control than younger (≤ 60 years) patients. Conclusions: Failure of oesophageal acid control in candidates for Barrett's oesophagus reversal on very high dose of proton pump inhibitor is not uncommon. Our study suggests that ambulatory 24‐h oesophageal pH monitoring should be considered in all candidates for Barrett's reversal who are treated with high dose proton pump inhibitor to ensure normalization of oesophageal acid exposure.