Reservoir compaction or shallow gas phenomena may cause offshore platforms to experience subsidence and deformation which could affect their structural integrity. Excessive subsidence may also cause loss of production as well as loss of live. However, the physical location of many offshore platforms which are typically hundreds of kilometers offshore poses a challenge to measure the subsidence rate accurately and in real-time. Over the years GNSS in the form of GPS has been used to determine such subsidence rate with great accuracy (cm level). The present GPS technology would not provide the monitoring in real-time mode. Present RTK GPS however has very serious limitation to be utilized in offshore due to its short range (approximately 50 km baselines) capabilities; typical offshore platforms are 150 km from shore. This paper therefore develops a new or improve RTK algorithm for longer range to be applied in real-time offshore platform monitoring. © 2016 Taylor & Francis Group, London.