17 May 2016

Sirius Minerals Plc

Polyhalite reserve increase

Sirius Minerals Plc (AIM: SXX, OTCQX: SRUXY) ('Sirius' or the 'Company')announces an increase in its Probable Ore Reserve ('the Reserve') at its North Yorkshire polyhalite project ('the Project').

The Reserve has increased to 280 million tonnes at an average grade of 88.4% from the previous level of 250 million tonnes of polyhalite at a grade of 87.8% (as announced on 18 September 2013). The Reserve has been reported in accordance with the 2012 Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves as published by the Joint Ore Reserves Committee of the Australasian Institute of Mining and Metallurgy, Australian Institute of Geoscientists and Minerals Council of Australia ('the JORC Code').

The increase in the Reserve results from the completion of the Definitive Feasibility Study ('DFS'), the results of which were announced on 17 March 2016, and the detailed work that has been completed on the mining schedule and resource by SRK Consulting (UK) Ltd ('SRK') as part of the DFS. Specifically it comprises the tonnage of mineralisation previously reported as an Indicated Mineral Resource which is planned to be mined and then transported to Teesside.

Chris Fraser, Managing Director and CEO of Sirius, comments:

'This increase, in what was already the world`s largest and highest quality polyhalite reserve, adds further confirmation of the outstanding nature of this deposit.'

SRK's Ore Reserve Statement for the Project is presented below. The economic viability of exploiting this has been confirmed by the DFS. This is a sub-set of the Indicated Mineral Resource (presented in the second table below) and not additive to this.

The previously reported Mineral Resource is tabled below illustrating the significant base that the Project has to build on once exploration drilling commences from underground. As with the Ore Reserve statement, SRK's Mineral Resource statement has also been reported using the terminology and guidelines set out in the JORC Code.

SRK considers that there is a good likelihood that a proportion of the currently reported Inferred Mineral Resource will be upgraded to the Indicated Mineral Resource and Ore Reserve status once the mine has been established and the polyhalite horizons have been accessed and underground exploration and grade control drilling commences. It also considers that additional Mineral Resources and Ore Reserves are likely to be generated following ongoing exploration and assessment during the mine life.

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About Sirius Minerals Plc

Sirius Minerals is the fertilizer development company focused on the development of its North Yorkshire polyhalite project, the United Kingdom. It has the world's largest and highest grade deposit of polyhalite, a multi-nutrient form of potash containing potassium, sulphur, magnesium and calcium. Incorporated in 2003, Sirius Minerals' shares are traded on the London Stock Exchange's AIM market. Its shares are also traded in the United States on the OTCQX through a sponsored ADR facility. Further information on the Company can be found at: www.siriusminerals.com.

Qualified Persons

The information in this press release that relates to Ore Reserves and Mineral Resources is based on information compiled under the direction of Dr Mike Armitage C Eng, who is a Member of the Institute of Materials, Minerals and Mining which is a 'Recognised Overseas Professional Organisation' (ROPO) included in a list promulgated by ASX from time to time.

Dr Armitage is a full time employee of SRK Consulting (UK) Ltd and has sufficient experience which is relevant to the style of mineralisation and type of deposit under consideration and to the activity which he has undertaken to qualify as a Competent Person as defined in the 2012 Edition of the 'Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves' (the JORC Code) and for the purposes of the AIM Rules. Dr Armitage has reviewed this press release and consents to the inclusion in the press release of the matters based on his information in the form and context in which this appears.

Graham Clarke, Operations Director for Sirius Minerals Plc, who has reviewed this Stock Exchange Announcement, has over 26 years' experience in the potash mining industry. He has a Degree in Mining Engineering from the University of Nottingham, is a Fellow of the Institute of Materials, Minerals and Mining (IMMM) and extensive operational experience gained at Cleveland Potash Limited in the mining of the Boulby Potash seam and the exploration and development of the upper Fordon Polyhalite seam.