SECURITIES AND EXCHANGE COMMISSION
                              Washington, DC 20549



                                    FORM 8-K



                             Current Report Pursuant
                          to Section 13 or 15(d) of the
                         Securities Exchange Act of 1934



    Date of report (Date of earliest event reported)        December 13, 1999
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                               UNOCAL CORPORATION
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             (Exact name of registrant as specified in its charter)



                                    Delaware
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                 (State or Other Jurisdiction of Incorporation)



    1-8483                                   95-3825062
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(Commission File Number)                (I.R.S. Employer Identification No.)



2141 Rosecrans Avenue, Suite 4000, El Segundo, California         90245
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(Address of Principal Executive Offices)                       (Zip Code)



                                 (310) 726-7600
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              (Registrant's Telephone Number, Including Area Code)


Item 5.      Other Events.


Mergers and Acquisitions
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         Unocal Corporation  (Unocal) and Titan  Exploration,  Inc. (Titan) have
entered  into an  agreement  to  merge  Unocal's  oil and  gas  exploration  and
production assets in the Permian and San Juan basins,  located in the West Texas
- - New Mexico area,  with Titan into a new  publicly  traded  company  named Pure
Energy Resources, Inc.

Pure  Energy  Resources  will  have   approximately  50  million  common  shares
outstanding upon the completion of the merger.  Unocal will hold 65 percent,  or
32.7  million  shares of the new company.  Upon  approving  the merger,  Titan's
stockholders will receive 0.4302 shares of Pure Energy Resources, Inc. stock for
every share of Titan they  currently  hold.  The  transaction  is expected to be
completed during the first quarter of 2000.

Jack D. Hightower,  current Chief Executive  Officer of Titan,  will be Chairman
and  Chief  Executive  Officer  of the new  company.  M. Jack  Rathbone,  former
President of Mobil Producing  Texas & New Mexico,  Inc., will assume the role of
Executive Vice President of Operations and Gary Dupriest, current Vice president
of  Unocal's  Permian  operations,  will  assume the role of Vice  president  of
Production.

Pure  Energy  Resources'  board of  directors  will  consist  of Mr.  Hightower,
Chairman;  Timothy H. Ling,  Unocal's Chief Financial Officer and Executive Vice
President for North American Energy Operations; George G. Staley, Executive Vice
President,  Exploration of Titan; Herbert C. Williamson,  III, energy consultant
and  former  managing  director  of  Credit  Suisse  First  Boston;  Graydon  H.
Laughbaum,  Jr.,  global energy  advisor and former Senior Vice President of New
Ventures for Unocal; H. D. Maxwell,  former President,  North American Oil & Gas
Division of Unocal, retired; and one additional Unocal affiliate director yet to
be named.

On  a   pro   forma   basis,   the   new   company   will   have   175   million
barrels-of-oil-equivalent  (BOE) in reserves (approximately 80 percent is proved
developed  producing) with net production of  approximately  40,000 BOE per day.
This production  consists of 60 percent natural gas and 40 percent oil on a 6 to
1 MCF per barrel ratio.

Unocal will report the financial and operating  results of Pure Energy Resources
on a consolidated basis.


Reserve Replacement Ratio and Finding, Development & Acquisition Costs
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         Unocal expects that it will replace  approximately  135-145  percent of
its  worldwide  oil and gas  production  with new  reserves  in 1999,  and total
finding, development and acquisition (FD&A) costs could be about $5.50-$6.00 per
BOE for the year.

The reserve  replacement  ratio reflects  discoveries and  extensions,  improved
recovery, price-related and other revisions, purchases of reserves, and sales of
reserves.  The company has not yet booked reserves associated with the deepwater
Mirage and Mad Dog discoveries in the Gulf of Mexico.

The estimated  reserve  replacement  ratio and the estimated  FD&A costs include
Northrock Resources Ltd. (Northrock). Excluding the minority share of Northrock,
the estimated  reserve  replacement  ratio is 120-130  percent and the estimated
FD&A costs are $6.50-$7.00 per BOE.

 Detailed  reserve  replacement  and  FD&A  data for  1999  are  expected  to be
published in February 2000.


Forward-looking statements regarding business and market transactions, pro-forma
estimates  of  reserves  and  production  and  estimates  regarding  the reserve
replacement  ratio,  possible  future reserve  bookings,  FD&A costs,  and other
exploration  and  production  activities in this filing are based on assumptions
concerning operational, market, competitive, regulatory, environmental and other
conditions  and  considerations.  Actual  results  could differ  materially as a
result of factors discussed in Unocal's 1998 Annual Report on Form 10-K.

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Pursuant  to the  requirements  of the  Securities  Exchange  Act of  1934,  the
registrant  has duly  caused  this  report  to be  signed  on its  behalf by the
undersigned, thereunto duly authorized.



                                                UNOCAL CORPORATION
                                                (Registrant)





Date:  December 15, 1999                        By:  /s/ JOE D. CECIL
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                                                Joe D. Cecil
                                                Vice President and Comptroller
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