Update - Horse Hill, UK Weald Basin

11 May 2015 Doriemus plc ("Doriemus" or the "Company") Upgrade to Horse Hill Conventional Portland Sandstone Oil in Place Volumes Doriemus plc (LSE AIM: DOR) is pleased to announce an upgrade to theconventional Stock Tank Oil Initially In Place ("STOIIP") volumes estimated forthe overall Upper Portland Sandstone conventional reservoir in the Horse Hill-1("HH-1") and Collendean Farm-1 ("CF-1") structure (`Horse Hill'), in thePEDL137 licence area (Surrey-West Sussex, Weald Basin). This revised STOIIP isseparate to the oil-in-place volumes estimated for the argillaceous limestonesand mudstones of the Kimmeridge, Oxford and Lias rock sections of the HH-1well, as reported on 9 April2015 and 15 April 2015. The Company has a netattributable interest of 6.5% in PEDL137. An independent study of the Portland Sandstone reservoir was conducted by XodusGroup ("Xodus"), an international energy consultancy based in the UK (seewww.xodusgroup.com), for the Horse Hill Developments Ltd (HHDL) main consortiumpartners UK Oil and Gas Investments PLC (UKOG). The study is based on newpetrophysical evaluations of both the HH-1 discovery and the older CollendeanFarm-1 ("CF-1") well plus an updated interpretation of 2D seismic data acrossthe Licence. The study report is available on UKOG's website (seewww.ukogplc.com). The HH-1 and CF-1 discoveries lie within an approximately 100-foot thick, UpperPortland Sandstone gross reservoir interval, within a 6km by 3km tilted faultblock structure as defined by 2D seismic. The crest of the Upper Portlandconventional oil discovery lies at approximately 1,760ft TVDSS, and extendsover a mapped maximum areal closure of approximately 2,000 acres. The UpperPortland reservoir is productive at the nearby Brockham field, some 9km NNW, inwhich UKOG has an indirect interest of 3.6%. Xodus calculate that the Upper Portland Sandstone conventional reservoircontains a "Best Estimate" (P50) gross STOIIP of 21.0 MMbbl, which is slightlymore than UKOG's own revised latest estimate of 20MMbbl, and which is entirelywithin PEDL137 and encompasses both the HH-1 and CF-1 wells. This is anincrease of 12.8 MMbbl over the 8.2 MMbbl (P50) gross STOIIP reported on 17December 2014, which results largely from the new petrophysical evaluation ofHH-1 electric logs, calibrated to new XRD and MICP data, and a newinterpretation of the CF-1 electric logs, calibrated to core data. The gross Upper Portland STOIIP ranges estimated by Xodus are as per the tablebelow: STOIIP (MMbbl) Low Best High Mean Upper Portland Gross 100% 14.3 21.0 30.4 21.8 The oil in place hydrocarbon volumes (STOIIP) estimated should not be construedas recoverable resources or reserves. Meaningful estimates of recoverable oilwithin the Upper Portland can likely only be made following the proposed HH-1flow test and a significant proportion will not be recovered during any futureproduction regime The Upper Portland is the uppermost, conventional oil-saturated reservoir foundin the HH-1 and CF-1 wells. It overlies, and is entirely separate from, theKimmeridge, Oxford and Lias oil-saturated argillaceous limestone and mudstonerock sections reported on 9 April 2015 and 15 April 2015. The Xodus study is an independent review, solely of the Upper PortlandSandstone trap-constrained conventional oil reservoir. It does not include anyassessment of the deeper Kimmeridge, Oxford and Lias oil-saturated argillaceouslimestone and mudstone rock sections, which are currently the subject of aseparate review by Nutech Ltd. Reporting Standards: Xodus' STOIIP volumes have been prepared in accordance with the 2007 PetroleumResources Management System prepared by the Oil and Gas Reserves Committee ofthe Society of Petroleum Engineers (SPE), reviewed, and jointly sponsored bythe World Petroleum Council (WPC), the American Association of PetroleumGeologists (AAPG) and the Society of Petroleum Evaluation Engineers (SPEE). Xodus state in their Executive Summary that; "In conducting this review Xodushas utilised information and interpretations supplied by UKOG, comprisingoperator information, geological, geophysical, petrophysical, well logs andother data along with various technical reports. Xodus has reviewed theinformation provided and modified assumptions where it considered this to beappropriate. Site visits were not considered necessary for the purposes of thisreport." Donald Strang, Doriemus' Chairman, commented: "The Xodus Report supports the Company's view that the Horse Hill andCollendean Farm oil pool constitutes a significant conventional Upper PortlandSandstone oil discovery in the Weald basin. Subject to approval by the relevant authorities, the Consortium intends to flowtest this conventional sandstone zone as part of a wider test programme of theHH-1 well later in 2015. A successful test would be followed by a fulltechnical resource assessment, and the identification of potentiallyrecoverable resource volumes. Subject to these results, the Company is informed that the operator, Horse HillDevelopments Ltd, intends to engage with the Oil and Gas Authority ("OGA") andother regulators, and seek to move the PEDL137 licence into the ProductionPeriod as soon as practicable, via submission of a Field Development Plan tothe OGA. The PEDL137 licence is currently in the exploration phase and expireson 30 September 2015. HHDL has applied for a one-year extension of theexploration phase to 30 September 2016." Doriemus' interest in Horse Hill: The Horse Hill-1 well is located within onshore exploration License PEDL137, onthe northern side of the Weald Basin near Gatwick Airport. Doriemus owns a 10%direct interest in Horse Hill Developments Ltd. HHDL is a special purposecompany that owns 65% participating interests and is the operator of licencePEDL137 and the adjacent licence PEDL246 in the UK Weald Basin. The remaining35% participating interests in the PEDL137 and PEDL246 licenses are held byMagellan Petroleum Corporation. For further information please contact: Doriemus plcDonald Strang/Hamish Harris +44 (0) 20 7440 0640 Cairn Financial Advisers LLP:James Caithie / Carolyn Sansom +44 (0) 20 7148 7900 Public Relations:Square 1 Consulting Ltd +44 (0) 20 7929 5599David Bick/Mark Longson Glossary: argillaceous a limestone containing a significant proportion of claylimestone minerals clastic rocks composed of broken pieces of older rocks Core a cylindrical sample of rock, obtained during drilling of wells and removed for inspection at surface Discovery a discovery is a petroleum accumulation for which one or several exploratory wells have established through testing, sampling and/or logging the existence of a significant quantity of potentially moveable hydrocarbons electric logs tools used within the wellbore to measure the rock and fluid properties of surrounding rock formations fault block a very large subsurface block of rock, created by tectonic and localised stresses limestone a carbonate sedimentary rock predominantly composed of calcite of organic, chemical or detrital origin. Minor amounts of dolomite, chert and clay are common in limestones. Chalk is a form of fine-grained limestone MICP mercury injection capillary pressure, a measure of rock porosity and permeability, from rock cores or cuttings, and a calibration of porosity logs MMbbl Million barrels mudstone an extremely fine-grained sedimentary rock consisting of a mixture of clay and silt-sized particles oil in place or oil the quantity of oil or petroleum that is estimated toinitially-in-place exist originally in naturally occurring accumulations before any extraction or production petrophysical the study of physical and chemical rock properties andevaluation their interactions with fluids; studies typically use well logs, well cores and seismic data P10 a 10% probability that a stated volume will be equalled or exceeded P50 a 50% probability that a stated volume will be equalled or exceeded P90 a 90% probability that a stated volume will be equalled or exceeded recovery or the quantity or portion of petroleum, here oil and gas,recoverable initially-in-place that can be extracted by a well or wells to the surface Resources the Society of Petroleum engineers ("SPE") defines as all quantities of petroleum, here oil and gas, which are estimated to be initially-in-place; however, some users consider only the estimated recoverable portion to constitute a resource. Reserves reserves are defined by the SPE as those quantities of petroleum, here oil and gas, which are anticipated to be commercially recovered from known accumulations from a given date forward. Reservoir a subsurface rock formation containing an individual natural accumulation of moveable petroleum that is confined by impermeable rock/formations sandstone a clastic sedimentary rock whose grains are predominantly sand-sized. The term is commonly used to imply consolidated sand or a rock made of predominantly quartz sand Seismic use of reflected and refracted sound waves generated at the surface to ascertain the nature of the subsurface geological structures. 2D seismic records a two dimensional cross-section through the subsurface collected using the two-dimensional common depth point method STOIIP stock tank oil initially in place TVDSS true vertical depth below a subsea datum XRD x-ray diffraction; scattering of x-rays by the atoms of a rock or crystal that gives information on the structure, composition and identity of the rock or crystal