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                                                                   EXHIBIT 10.10

                          REGISTRATION RIGHTS AGREEMENT

         THIS REGISTRATION RIGHTS AGREEMENT ("Agreement"), is made and entered
into as of the 18th day of March, 2000, by and among RENTECH, INC., a Colorado
corporation (the "Company"), and FOREST OIL CORPORATION and ANSCHUTZ INVESTMENT
COMPANY (each of whom is individually referred to as a "Purchaser" and all of
whom collectively are referred to as the "Purchasers"). Capitalized terms used
in this Agreement and not otherwise defined herein shall have the meanings
ascribed to them in the Purchase Agreements (as defined below).


                                   BACKGROUND

         In connection with the consummation of the transactions contemplated by
those certain Stock Purchase Agreements (the "Purchase Agreements") of even date
herewith by and between the Company and each of the Purchasers respectively in
connection with a private placement by the Company pursuant to Rule 506 under
Regulation D of the Securities Act of 1933, as amended, and the rules and
regulations thereunder, or any similar successor statute (the "1933 Act"), the
Company has agreed, upon the terms and subject to the conditions of the Purchase
Agreements, to issue and sell to each of the Purchasers 1,000,000 shares of
Common Stock (the "Purchased Common Shares") and to issue stock options (the
"Options") to each of the Purchasers for the purchase by each Purchaser of an
aggregate of 3,000,000 shares of Common Stock (as the same may be adjusted in
accordance with the agreements governing such options, the "Option Shares").
Collectively, the Purchased Common Shares and the Option Shares are hereinafter
collectively referred to as the "Purchased Securities". To induce Purchasers to
execute and deliver their respective Purchase Agreements, the Company has agreed
to file a Registration Statement covering the Purchased Common Shares and the
Option Shares under the 1933 Act and applicable state securities laws.

         For and in consideration of the background circumstances and the mutual
covenants contained herein and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the Company and the
Purchasers hereby agree as follows:


         SECTION 1. DEFINITIONS.

         As used in this Agreement, the following capitalized terms are used
with the meanings there after ascribed.

                  (a) "Investor" means any Purchaser and any permitted
         transferee or assignee thereof to whom any Purchaser assigns its rights
         under this Agreement and who agrees to become bound by the provisions
         of this Agreement in accordance with Section 9.

                  (b) "Person" means a corporation, a limited liability company,
         an association, a partnership, an organization, a business, an
         individual, a governmental or political subdivision thereof, or a
         governmental agency.


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                  (c) "Register," "Registered," and "Registration" refer to a
         registration effected by preparing and filing one or more Registration
         Statements in compliance with the 1933 Act and pursuant to Rule 415
         under the 1933 Act or any successor rule providing for offering
         securities on a continuous basis ("Rule 415"), and the declaration or
         ordering of effectiveness of such Registration Statement(s) by the
         United States Securities and Exchange Commission (the "SEC").

                  (d) "Registrable Securities" means the Purchased Common
         Shares, and the Option Shares and any shares of capital stock issued or
         issuable with respect to the Purchased Securities or the Option Shares
         as a result of any sale or issuance of Common Stock by the Company for
         less than its then prevailing fair market value, any stock split, stock
         dividend, recapitalization, exchange, or similar event.

                  (e) "Registration Statement" means a registration statement of
         the Company filed under the 1933 Act. Capitalized terms used herein and
         not otherwise defined herein shall have the respective meanings set
         forth in the Purchase Agreement.

         SECTION 2. REGISTRATION.

                  (a) MANDATORY REGISTRATION. (i) The Company shall use its best
         efforts to prepare, and, on or before the date that is thirty (30) days
         after the date hereof, file with the SEC a Registration Statement or
         Registration Statements (as necessary) on Form S-3 (or, if such form is
         unavailable for such a registration, on such other form as is available
         for such a registration of all of the Registrable Securities) (any of
         which may contain a combined prospectus with other registrations by the
         Company), covering the resale of all of the Registrable Securities,
         which Registration Statement(s), to the extent allowable under the 1933
         Act and the rules promulgated thereunder (including without limitation
         Rule 416), shall state that such Registration Statement(s) also covers
         such indeterminate number of additional shares (the "Indeterminate
         Shares") of Common Stock as may become issuable upon the adjustment of
         the Options as the result of any sale or issuance of Common Stock by
         the Company for less than its then prevailing fair market value or any
         stock splits, stock dividends or similar transactions requiring
         adjustment of the number of Option Shares issuable upon the exercise or
         conversion of the Options in accordance with the Option Agreements.

                           (ii) To the extent the Indeterminate Shares for any
         reason cannot be registered under the Registration Statement(s)
         required under Section 2(a)(i) above, then with respect to such
         Indeterminate Shares, the Company shall use its best efforts to
         prepare, and, on or before the date that is thirty (30) days after the
         Indeterminate Shares become issuable, file with the SEC a Registration
         Statement or Registration Statements (as necessary) on Form S-3 (or, if
         such form is unavailable for such a registration, on such other form as
         is available for such a registration of all of the Indeterminate
         Shares) (any of which may contain a combined prospectus with other
         registrations by the Company), covering the resale of all of the
         Indeterminate Shares.

                           (iii) A copy of the Registration Statement(s) (and
         each amendment or supplement thereto, and each request for acceleration
         of effectiveness thereof) shall be provided to (and subject to the
         approval of the Investors, which approval shall not be unreasonably
         withheld or denied) the Investors and their counsel prior to its filing
         or other submission.


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                           (iv) The Company shall use its best efforts to obtain
         effectiveness of the Registration Statement(s) as soon as practicable.

                  (b) MAINTENANCE OF EFFECTIVENESS; REGISTRATION PERIOD. The
         Company shall use its best efforts to cause the Registration
         Statement(s) relating to the Registrable Securities filed in accordance
         with Section 2(a) to become effective as soon as possible after such
         filing, but in no event later than the Registration Deadline (as
         defined below), and to keep the Registration Statement(s) effective
         pursuant to Rule 415 at all times until the earlier of (i) the date on
         which all of the Registrable Securities have been sold (and no further
         Registrable Securities may be issued in the future) or (ii) the date as
         of which the Investors may immediately sell all of the Registrable
         Securities without restriction pursuant to Rule 144 promulgated under
         the 1933 Act (or successor thereto) or otherwise, not to exceed seven
         (7) years from the effective date(s) of the Registration Statement(s)
         (the "Registration Period").

                  (c) PIGGY-BACK REGISTRATIONS. If at any time prior to the
         expiration of the Registration Period the Company proposes to file with
         the SEC a Registration Statement relating to an offering for its own
         account or the account of others under the 1933 Act of any of its
         securities (other than on Form S-4 or Form S-8 or their then
         equivalents relating to securities to be issued solely in connection
         with any acquisition of any entity or business or equity securities
         issuable in connection with stock option or other employee benefit
         plans) the Company shall promptly send to each Investor who holds
         Registrable Securities written notice of the Company's intention to
         file a Registration Statement and of such Investor's rights under this
         Section 2(c) and, if within twenty (20) days after receipt of such
         notice, such Investor shall so request in writing, the Company shall
         include in such Registration Statement all or any part of the
         Registrable Securities that such Investor requests to be registered,
         subject to the priorities set forth in Section 2(d) below. No right to
         registration of Registrable Securities under this Section 2(c) shall be
         construed to limit any registration required under Section 2(a) hereof.
         The obligations of the Company under this Section 2(c) may be waived by
         each individual Investor holding Registrable Securities, in its sole
         discretion, without effect to any other Investor. If an offering in
         connection with which an Investor is entitled to registration under
         this Section 2(c) is an underwritten offering, then each Investor whose
         Registrable Securities are included in such Registration Statement
         shall, unless otherwise agreed by the Company, offer and sell such
         Registrable Securities in an underwritten offering using the same
         underwriter or underwriters and, subject to the provisions of this
         Agreement, on the same terms and conditions as other shares of Common
         Stock included in such underwritten offering.

                  (d) PRIORITY IN PIGGY-BACK REGISTRATION RIGHTS. If the
         registration referred to in Section 2(c) is to be an underwritten
         public offering for the account of the Company and the managing
         underwriter(s) advise the Company in writing that, in their reasonable
         good faith opinion, marketing or other factors dictate that a
         limitation on the number of shares of Common Stock which may be
         included in the Registration Statement is necessary to facilitate and
         not adversely affect the proposed offering, then the Company shall
         include in such registration: (i) first, all securities the Company
         proposes to sell for its own account, (ii) second, up to the full
         number of securities proposed to be registered for the account of the
         holders of securities entitled to inclusion of their securities in the
         Registration Statement by reason of demand registration rights, (iii)
         third, the securities requested to be registered by the Investors, pro
         rata based on the number of Registrable Shares each has requested to be
         included in such registration, and (iv) fourth, the other holders of
         securities entitled to participate in the registration, drawn from them
         pro rata based on the number each has requested to be included in such
         registration.


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                  (e) ELIGIBILITY FOR FORM S-3. The Company represents, warrants
         and covenants that it has filed and shall file all reports required to
         be filed by the Company with the SEC in a timely manner so as to obtain
         and maintain such eligibility for the use of Form S-3. In the event
         that Form S-3 is not available for sale by the Investors of the
         Registrable Securities, then (i) the Company, with the consent of each
         Investor pursuant to Section 2(a), shall register the sale of the
         Registrable Securities on another appropriate form, such as Form SB-2,
         and (ii) the Company shall undertake to register the Registrable
         Securities on Form S-3 as soon as such form is available.

                  (f) LOCK-UP PERIOD. Each Purchaser agrees (y) not to offer,
         sell, contract to sell or otherwise dispose of any of its Purchased
         Common Shares during the 90-day period beginning on the date of the
         closing of its respective Purchase Agreement, and (z) upon the
         expiration of the aforesaid 90-day period, not to offer, sell, contract
         to sell or otherwise dispose of more than 50% of its Purchased Common
         Shares for an additional 90-day period beginning on the day following
         the expiration of the aforesaid 90-day period.


         SECTION 3. RELATED OBLIGATIONS.

         Whenever an Investor has requested that any Registrable Securities be
registered pursuant to Section 2(c) hereof, or at such time as the Company is
obligated to file a Registration Statement with the SEC pursuant to Section 2(a)
hereof, the Company will use its best efforts to effect the registration of the
Registrable Securities in accordance with the respective method of disposition
thereof as required by such provisions and, pursuant thereto, and the Company
shall have the following obligations:

                  (a) The Company shall promptly prepare and file with the SEC a
         Registration Statement with respect to the Registrable Securities
         within the time provided in Section 2(a) for the registration of
         Registrable Securities pursuant to Section 2(a) or Section 2(c), if
         applicable, and use its best efforts to cause such Registration
         Statement(s) relating to Registrable Securities to become effective as
         soon as possible after such filing and in any event within sixty (60)
         days after filing with the SEC (the "Registration Deadline") and
         provided further that the Registration Deadline shall not exceed ninety
         (90) days from the date hereof, and keep the Registration Statement(s)
         effective pursuant to Rule 415 at all times until the completion of the
         Registration Period. The Registration Statement(s) (including any
         amendments or supplements thereto and prospectuses contained therein)
         shall not contain any untrue statement of a material fact or omit to
         state a material fact required to be stated therein, or necessary to
         make the statements therein, in light of the circumstances in which
         they were made, not misleading.

                  (b) The Company shall prepare and file with the SEC such
         amendments (including post-effective amendments) and supplements to the
         Registration Statement(s) and the prospectus(es) used in connection
         with the Registration Statement(s), which prospectus(es) are to be
         filed pursuant to Rule 424 promulgated under the 1933 Act, as may be
         necessary to keep the Registration Statement(s) effective at all times
         during the Registration Period, and, during such period, comply with
         the provisions of the 1933 Act with respect to the disposition of all
         Registrable Securities of the Company covered by the Registration
         Statement(s) until such time as all of such Registrable Securities
         shall have been disposed of in accordance with the intended methods of
         disposition by the seller or sellers thereof as set forth in the
         Registration Statement(s). In the event the number of shares available
         under a Registration Statement filed pursuant to this Agreement is
         insufficient to


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         cover all of the Registrable Securities, the Company shall amend the
         Registration Statement, or file a new Registration Statement (on the
         short form available therefor, if applicable), or both, so as to cover
         all of the Registrable Securities, in each case, as soon as
         practicable, but in any event within fifteen (15) days after the
         necessity therefor arises (based on the market price of the Common
         Stock and other relevant factors on which the Company reasonably elects
         to rely) or upon reasonable request therefor by any Investor. The
         Company shall use its best efforts to cause such amendment and/or new
         Registration Statement to become effective as soon as practicable
         following the filing thereof. For purposes of the foregoing provision,
         the number of shares available under a Registration Statement shall be
         deemed "insufficient to cover all of the Registrable Securities" if at
         any time the number of Registrable Securities issued or issuable is in
         excess of the number of shares of Common Stock eligible for resale
         under the then effective Registration Statement(s) filed to cover the
         Registrable Securities in accordance with this Agreement.

                  (c) The Company shall furnish to each Investor whose
         Registrable Securities are included in the Registration Statement(s)
         and its legal counsel, without charge, (i) promptly after the same is
         prepared and filed with the SEC, at least one copy of the Registration
         Statement and any amendment thereto, including financial statements and
         schedules, all documents incorporated therein by reference, and all
         exhibits, the prospectus(es) included in such Registration Statement(s)
         (including each preliminary prospectus) and all correspondence by or on
         behalf of the Company to the SEC or the staff of the SEC and all
         correspondence from the SEC or the staff of the SEC to the Company or
         its representatives, related to such Registration Statement(s), (ii)
         upon the effectiveness of any Registration Statement, such number of
         copies of the prospectus included in such Registration Statement and
         all amendments and supplements thereto as such Investor may reasonably
         request, and (iii) such other documents, including any preliminary
         prospectus, as such Investor may reasonably request in order to
         facilitate the disposition of the Registrable Securities owned by such
         Investor.

                  (d) The Company shall (i) register and qualify the Registrable
         Securities covered by the Registration Statement(s) under such other
         securities or "blue sky" laws of such jurisdictions in the United
         States as any Investor reasonably requests, (ii) prepare and file in
         those jurisdictions, such amendments (including post-effective
         amendments) and supplements to such registrations and qualifications as
         may be necessary to maintain the effectiveness thereof during the
         Registration Period, (iii) take such other actions as may be necessary
         to maintain such registrations and qualifications in effect at all
         times during the Registration Period, and (iv) take all other actions
         reasonably necessary or advisable to qualify the Registrable Securities
         for sale in such jurisdictions, Provided that the Company shall not be
         required in connection therewith or as a condition thereto to qualify
         to do business or to file a general consent to service of process in
         any such states or jurisdictions, and further provided that (anything
         in this Section to the contrary notwithstanding with respect to the
         bearing of expenses) if any jurisdiction in which the securities shall
         be qualified shall require that expenses incurred in connection with
         the qualification of the securities in that jurisdiction be borne by
         selling shareholders pro rata, to the extent required by such
         jurisdiction. The Company shall promptly notify each Investor who holds
         Registrable Securities of the receipt by the Company of any
         notification with respect to the suspension of the registration or
         qualification of any of the Registrable Securities for sale under the
         securities or "blue sky" laws of any jurisdiction in the United States
         or its receipt of actual notice of the initiation or threatening of any
         proceeding for such purpose.

                  (e) In the event Investors who hold a majority of the
         Registrable Securities being offered in the offering select
         underwriters for the offering, the Company shall enter into and perform
         its


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         obligations under an underwriting agreement, in usual and customary
         form, including, without limitation, customary indemnification and
         contribution obligations, with the underwriters of such offering.

                  (f) As promptly as practicable after becoming aware of such
         event, the Company shall notify each Investor in writing of the
         happening of any event, of which the Company has knowledge, as a result
         of which, the prospectus included in a Registration Statement, as then
         in effect, includes an untrue statement of a material fact or omission
         to state a material fact required to be stated therein or necessary to
         make the statements therein, in light of the circumstances under which
         they were made, not misleading, and promptly prepare a supplement or
         amendment to the Registration Statement to correct such untrue
         statement or omission, and deliver such number of copies of such
         supplement or amendment to each Investor as such Investor may
         reasonably request. The Company shall also promptly notify each
         Investor in writing (i) when a prospectus or any prospectus supplement
         or post-effective amendment has been filed, and when a Registration
         Statement or any post-effective amendment has become effective
         (notification of such effectiveness shall be delivered to each Investor
         by facsimile by the next business day of such effectiveness and by
         overnight mail), (ii) of any request by the SEC for amendments or
         supplements to a Registration Statement or related prospectus or
         related information, and (iii) of the Company's reasonable
         determination that a post-effective amendment to a Registration
         Statement would be appropriate.

                  (g) The Company shall use its best efforts to prevent the
         issuance of any stop order or other suspension of effectiveness of a
         Registration Statement, or the suspension of the qualification of any
         of the Registrable Securities for sale in any jurisdiction and, if such
         an order or suspension is issued, to obtain the withdrawal of such
         order or suspension at the earliest possible moment, and to notify each
         Investor who holds Registrable Securities being sold (and, in the event
         of an underwritten offering, the managing underwriters) of the issuance
         of such order and the resolution thereof, or its receipt of actual
         notice of the initiation, or threatened initiation of any proceeding
         for such purpose.

                  (h) The Company shall permit each Investor a single firm of
         counsel or such other counsel as thereafter designated as selling
         stockholders' counsel by the Investors who hold a majority of the
         Registrable Securities being sold, to review and comment upon the
         Registration Statement(s) and all amendments and supplements thereto at
         least seven (7) days prior to their filing with the SEC, and not file
         any document in a form to which such counsel reasonably objects. The
         Company shall not submit a request for acceleration of the
         effectiveness of a Registration Statement(s) or any amendment or
         supplement thereto without the prior approval of such counsel, which
         consent shall not be unreasonably withheld.

                  (i) At the request of the Investors who hold a majority of the
         Registrable Securities being sold, the Company shall furnish, on the
         date that Registrable Securities are delivered to an underwriter, if
         any, for sale in connection with the Registration Statement (i) if
         required by an underwriter, a letter, dated such date, from the
         Company's independent certified public accountants in form and
         substance as is customarily given by independent certified public
         accountants to underwriters in an underwritten public offering,
         addressed to the underwriters, and (ii) an opinion, dated as of such
         date, of counsel representing the Company for purposes of such
         Registration Statement, in form, scope, and substance as is customarily
         given in an underwritten public offering, addressed to the underwriters
         and the Investors.


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                  (j) The Company shall make available for inspection by (i) any
         Investor, (ii) any underwriter participating in any disposition
         pursuant to a Registration Statement, (iii) one firm of attorneys and
         one firm of accountants or other agents retained by each Investor, and
         (iv) one firm of attorneys retained by all such underwriters
         (collectively, the "Inspectors") all pertinent financial and other
         records, and pertinent corporate documents and properties of the
         Company (collectively, the "Records"), as shall be reasonably deemed
         necessary by each Inspector to enable each Inspector to exercise its
         due diligence responsibility, and cause the Company's officers,
         directors, and employees to supply all information which any Inspector
         may reasonably request for purposes of such due diligence; Provided
         However, that each Inspector shall hold in strict confidence and shall
         not make any disclosure (except to an Investor) or use of any Record or
         other information which the Company determines in good faith to be
         confidential, and of which determination the Inspectors are so
         notified, unless (A) the disclosure of such Records is necessary to
         avoid or correct a misstatement or omission in any Registration
         Statement or is otherwise required under the 1933 Act, (B) the release
         of such Records is ordered pursuant to a final, non-appealable subpoena
         or order from a court or government body of competent jurisdiction, or
         (C) the information in such Records has been made generally available
         to the public other than by disclosure in violation of this or any
         other agreement. Each Investor agrees that it shall, upon learning that
         disclosure of such Records is sought in or by a court or governmental
         body of competent jurisdiction or through other means, give prompt
         notice to the Company and allow the Company, at its expense, to
         undertake appropriate action to prevent disclosure of, or to obtain a
         protective order for, the Records deemed confidential.

                  (k) The Company shall hold in confidence and not make any
         disclosure of information concerning an Investor provided to the
         Company unless (i) disclosure of such information is necessary to
         comply with federal or state securities laws, (ii) the disclosure of
         such information is necessary to avoid or correct a misstatement or
         omission in any Registration Statement, (iii) the release of such
         information is ordered pursuant to a subpoena or other final,
         non-appealable order from a court or governmental body of competent
         jurisdiction, or (iv) such information has been made generally
         available to the public other than by disclosure in violation of this
         or any other agreement. The Company agrees that it shall, upon learning
         that disclosure of such information concerning an Investor is sought in
         or by a court or governmental body of competent jurisdiction or through
         other means, give prompt written notice to such Investor and allow such
         Investor, at the Investor's expense, to undertake appropriate action to
         prevent disclosure of, or to obtain a protective order for, such
         information.

                  (l) The Company shall use its best efforts to secure the
         inclusion for quotation on the Over the Counter Bulletin Board for the
         Registrable Securities, and, to arrange for at least two market makers
         to register with the National Association of Securities Dealers, Inc.
         ("NASD") as such with respect to such Registrable Securities. The
         Company shall pay all fees and expenses in connection with satisfying
         its obligation under this Section 3(l).

                  (m) The Company shall cooperate with the Investors who hold
         Registrable Securities being offered and, to the extent applicable, any
         managing underwriter or underwriters, to facilitate the timely
         preparation and delivery of certificates (not bearing any restrictive
         legend) representing the Registrable Securities to be offered pursuant
         to a Registration Statement and enable such certificates to be in such
         denominations or amounts, as the case may be, as any managing
         underwriter or underwriters or the Investors may reasonably request and
         registered in such names as the managing underwriter or underwriters,
         if any, or the Investors may request. Not later than the date on which
         any Registration Statement registering the resale of Registrable
         Securities is declared effective, the


<PAGE>   8


         Company shall deliver to its transfer agent instructions, accompanied
         by any reasonably required opinion of counsel, that permit sales of
         unlegended securities in a timely fashion that complies with then
         mandated securities settlement procedures for regular way market
         transactions.

                  (n) The Company shall take all other reasonable actions
         necessary to expedite and facilitate disposition by the Investors of
         Registrable Securities pursuant to a Registration Statement.

                  (o) The Company shall provide a transfer agent and registrar
         of all such Registrable Securities not later than the effective date of
         such Registration Statement.

                  (p) If requested by the managing underwriters or an Investor,
         the Company shall promptly incorporate in a prospectus supplement or
         post-effective amendment such information as the managing underwriters
         and the Investors agree should be included therein relating to the sale
         and distribution of Registrable Securities, including, without
         limitation, information with respect to the number of Registrable
         Securities being sold to such underwriters, the purchase price being
         paid therefor by such underwriters, and with respect to any other terms
         of the underwritten (or best efforts underwritten) offering of the
         Registrable Securities to be sold in such offering; make all required
         filings of such prospectus supplement or post-effective amendment as
         soon as notified of the matters to be incorporated in such prospectus
         supplement or post-effective amendment; and supplement or make
         amendments to any Registration Statement if requested by a shareholder
         or any underwriter of such Registrable Securities.

                  (q) The Company shall use its best efforts to cause the
         Registrable Securities covered by the applicable Registration Statement
         to be registered with or approved by such other governmental agencies
         or authorities as may be necessary to consummate the disposition of
         such Registrable Securities.

                  (r) The Company shall otherwise use its best efforts to comply
         with all applicable rules and regulations of the SEC in connection with
         any registration hereunder.


         SECTION 4. OBLIGATIONS OF THE INVESTORS.

                  (a) At least seven (7) days prior to the first anticipated
         filing date of the Registration Statement(s), the Company shall notify
         each Investor in writing of the information the Company requires from
         each such Investor if such Investor elects to have any of such
         Investor's Registrable Securities included in the Registration
         Statement(s). It shall be a condition precedent to the obligations of
         the Company to complete the registration pursuant to this Agreement
         with respect to the Registrable Securities of a particular Investor
         that such Investor shall furnish to the Company such information
         regarding itself, the Registrable Securities held by it, and the
         intended method of disposition of the Registrable Securities held by it
         as shall be reasonably required to effect the registration of such
         Registrable Securities, and shall execute such documents in connection
         with such registration as the Company may reasonably request.

                  (b) Each Investor by such Investor's acceptance of the
         Registrable Securities agrees to cooperate with the Company as
         reasonably requested by the Company in connection with the preparation
         and filing of the Registration Statement(s) hereunder, unless such
         Investor has notified


<PAGE>   9


         the Company in writing of such Investor's election to exclude all of
         such Investor's Registrable Securities from the Registration
         Statement(s).

                  (c) In the event Investors holding a majority of the
         Registrable Securities being registered determine to engage the
         services of an underwriter, each Investor agrees to enter into and
         perform such Investor's obligations under an underwriting agreement, in
         usual and customary form, including, without limitation, customary
         indemnification and contribution obligations, with the managing
         underwriter of such offering and take such other actions as are
         reasonably required in order to expedite or facilitate the disposition
         of the Registrable Securities, unless such Investor notifies the
         Company in writing of such Investor's election to exclude all of such
         Investor's Registrable Securities from the Registration Statement(s).

                  (d) Each Investor agrees that, upon receipt of any notice from
         the Company of the happening of any event of the kind described in
         Section 3(g) or the first sentence of 3(f), such Investor will
         immediately discontinue disposition of Registrable Securities pursuant
         to the Registration Statement(s) covering such Registrable Securities
         until such Investor's receipt of the copies of the supplemented or
         amended prospectus contemplated by Section 3(g) or the first sentence
         of 3(f) and, if so directed by the Company, such Investor shall deliver
         to the Company (at the expense of the Company) or destroy all copies in
         such Investor's possession, of the prospectus covering such Registrable
         Securities current at the time of receipt of such notice.

                  (e) No Investor may participate in any underwritten
         registration hereunder unless such Investor (i) agrees to sell such
         Investor's Registrable Securities on the basis provided in any
         underwriting arrangements approved by the Investors entitled hereunder
         to approve such arrangements, (ii) completes and executes all
         questionnaires, powers of attorney, indemnities, underwriting
         agreements, and other documents reasonably required under the terms of
         such underwriting arrangements, and (iii) agrees to pay its pro rata
         share of all underwriting discounts and commissions.


         SECTION 5. EXPENSES OF REGISTRATION.

         All expenses incurred in connection with registrations, filings, or
qualifications pursuant to Sections 2 and 3, including, without limitation, all
registration, listing and qualifications fees, printers and printing fees,
accounting fees, and fees and disbursements of counsel for the Company and fees
and disbursements of one counsel for the Investors, shall be borne by the
Company.


         SECTION 6. INDEMNIFICATION.

         In the event any Registrable Securities are included in a Registration
Statement under this Agreement:

                  (a) The Company will, and hereby does, indemnify, hold
         harmless, and defend each Investor who holds such Registrable
         Securities, the directors, officers, partners, employees, agents, and
         each Person, if any, who controls any Investor within the meaning of
         the 1933 Act or the Securities Exchange Act of 1934, as amended (the
         "1934 ACT"), and any underwriter (as defined in the 1933 Act) for the
         Investors, and the directors and officers of, and each Person, if any,
         who


<PAGE>   10


         controls, any such underwriter within the meaning of the 1933 Act or
         the 1934 Act (each, an "Indemnified Person"), against any losses,
         claims, damages, liabilities, judgments, fines, penalties, charges,
         costs, attorneys' fees, amounts paid in settlement or expenses, joint
         or several (collectively, "Claims") incurred in investigating,
         preparing, or defending any action, claim, suit, inquiry, proceeding,
         investigation, or appeal taken from the foregoing by or before any
         court or governmental, administrative, or other regulatory agency, body
         or the SEC, whether pending or threatened, whether or not an
         indemnified party is or may be a party thereto ("Indemnified Damages"),
         to which any of them may become subject insofar as such Claims (or
         actions or proceedings, whether commenced or threatened, in respect
         thereof) arise out of or are based upon: (i) any untrue statement or
         alleged untrue statement of a material fact in a Registration Statement
         or any post-effective amendment thereto or in any filing made in
         connection with the qualification of the offering under the securities
         or other "blue sky" laws of any jurisdiction in which Registrable
         Securities are offered ("Blue Sky Filing"), or the omission or alleged
         omission to state a material fact required to be stated therein or
         necessary to make the statements therein, in light of the circumstances
         under which the statements therein were made, not misleading, (ii) any
         untrue statement or alleged untrue statement of a material fact
         contained in any preliminary prospectus if used prior to the effective
         date of such Registration Statement, or contained in the final
         prospectus (as amended or supplemented, if the Company files any
         amendment thereof or supplement thereto with the SEC) or the omission
         or alleged omission to state therein any material fact necessary to
         make the statements made therein, in light of the circumstances under
         which the statements therein were made, not misleading, or, (iii) any
         violation or alleged violation by the Company of the 1933 Act, the 1934
         Act, any other law, including, without limitation, any state securities
         law, or any rule or regulation thereunder relating to the offer or sale
         of the Registrable Securities pursuant to a Registration Statement (the
         matters in the foregoing clauses (i) through (iii) being, collectively,
         "Violations"). Subject to the restrictions set forth in Section 6(d)
         with respect to the number of legal counsel, the Company shall
         reimburse the Investors and each such underwriter or controlling
         person, promptly as such expenses are incurred and are due and payable,
         for reasonable legal fees or other expenses incurred by them in
         connection with investigating or defending any such Claim.

         Notwithstanding anything to the contrary contained herein, the
         indemnification agreement contained in this Section 6(a): (i) shall not
         apply to a Claim arising out of or based upon a Violation which occurs
         in reliance upon and in conformity with information furnished in
         writing to the Company by any Indemnified Person or underwriter for
         such Indemnified Person expressly for use in connection with the
         preparation of the Registration Statement(s) or any such amendment
         thereof or supplement thereto, if such prospectus was timely made
         available by the Company pursuant to Section 3(c); (ii) with respect to
         any preliminary prospectus, shall not inure to the benefit of any such
         person from whom the person asserting any such Claim purchased the
         Registrable Securities that are the subject thereof (or to the benefit
         of any person controlling such person) if the untrue statement or
         mission of material fact contained in the preliminary prospectus was
         corrected in the prospectus, as then amended or supplemented, if such
         prospectus was timely made available by the Company pursuant to Section
         3(c), and the Indemnified Person was promptly advised in writing not to
         use the incorrect prospectus prior to the use giving rise to a
         violation and such Indemnified Person, notwithstanding such advice,
         used the incorrect prospectus; (iii) shall not be available to the
         extent such Claim is based on a failure of the Investor to deliver or
         to cause to be delivered the prospectus made available by the Company;
         and (iv) shall not apply to amounts paid in settlement of any Claim if
         such settlement is effected without the prior written consent of the
         Company, which consent shall not be unreasonably withheld. Such
         indemnity shall remain in full force and effect regardless of any


<PAGE>   11


         investigation made by or on behalf of the Indemnified Person and shall
         survive the transfer of the Registrable Securities by the Investors
         pursuant to Section 9.

                  (b) The Company shall be entitled to receive indemnities from
         underwriters, selling brokers, dealer managers, and similar securities
         industry professionals participating in any distribution, to the same
         extent as provided above, with respect to information such persons so
         furnished in writing expressly for inclusion in the Registration
         Statement(s).

                  (c) Promptly after receipt by an Indemnified Person under this
         Section 6 of notice of the commencement of any action or proceeding
         (including any governmental action or proceeding) involving a Claim,
         such Indemnified Person shall, if a Claim in respect thereof is to be
         made against any indemnifying party under this Section 6, deliver to
         the indemnifying party a written notice of the commencement thereof and
         the indemnifying party shall have the right to participate in, and, to
         the extent the indemnifying party so desires, jointly with any other
         indemnifying party similarly noticed, to assume control of the defense
         thereof with counsel mutually satisfactory to the indemnifying party
         and the Indemnified Person; Provided However, that an Indemnified
         Person shall have the right to retain its own counsel with the fees and
         expenses to be paid by the indemnifying party, if, in the reasonable
         opinion of counsel retained by the indemnifying party, the
         representation by such counsel of the Indemnified Person and the
         indemnifying party would be inappropriate due to actual or potential
         differing interests between such Indemnified Person and any other party
         represented by such counsel in such proceeding. The Company shall pay
         reasonable fees for only one separate legal counsel for the Investors,
         and such legal counsel shall be selected by the Investors holding a
         majority in interest of the Registrable Securities included in the
         Registration Statement to which the Claim relates. The Indemnified
         Person shall cooperate fully with the indemnifying party in connection
         with any negotiation or defense of any such action or claim by the
         indemnifying party and shall furnish to the indemnifying party all
         information reasonably available to the Indemnified Person which
         relates to such action or claim. The indemnifying party shall keep the
         Indemnified Person fully apprised at all times as to the status of the
         defense or any settlement negotiations with respect thereto. No
         indemnifying party shall be liable for any settlement of any action,
         claim or proceeding effected without its written consent, Provided
         However, that the indemnifying party shall not unreasonably withhold,
         delay or condition its consent. No indemnifying party shall, without
         the consent of the Indemnified Person, consent to entry of any judgment
         or enter into any settlement or other compromise which does not include
         as an unconditional term thereof the giving by the claimant or
         plaintiff to such Indemnified Person of a release from all liability in
         respect to such claim or litigation. Following indemnification as
         provided for hereunder, the indemnifying party shall be subrogated to
         all rights of the Indemnified Person with respect to all third parties,
         firms, or corporations relating to the matter for which indemnification
         has been made. The failure to deliver written notice to the
         indemnifying party within a reasonable time of the commencement of any
         such action shall not relieve such indemnifying party of any liability
         to the Indemnified Person under this Section 6, except to the extent
         that the indemnifying party is prejudiced in its ability to defend such
         action.

                  (d) The indemnification required by this Section 6 shall be
         made by periodic payments of the amount thereof during the course of
         the investigation or defense, as and when bills are received or
         Indemnified Damages are incurred.


<PAGE>   12


                  (e) The indemnity agreements contained herein shall be in
         addition to (i) any cause of action or similar right of the Indemnified
         Person against the indemnifying party or others, and (ii) any
         liabilities the indemnifying party may be subject to pursuant to the
         law.


         SECTION 7. CONTRIBUTION.

         To the extent any indemnification by an indemnifying party is
prohibited or limited by law, the indemnifying party agrees to make the maximum
contribution with respect to any amounts for which it would otherwise be liable
under Section 6 to the fullest extent permitted by law; provided however, that:
(i) no contribution shall be made under circumstances where the party against
whom indemnification is otherwise sought would not have been liable for
indemnification under the fault standards set forth in Section 6; (ii) no seller
of Registrable Securities guilty of fraudulent misrepresentation (within the
meaning of Section 11(f) of the 1933 Act) shall be entitled to contribution from
any seller of Registrable Securities who was not guilty of fraudulent
misrepresentation, and (iii) contribution by any seller of Registrable
Securities shall be limited in amount to the net amount of proceeds received by
such seller from the sale of such Registrable Securities.


         SECTION 8. REPORTS UNDER THE 1934 ACT.

         With a view to making available to the Investors the benefits of Rule
144 promulgated under the 1933 Act or any other similar rule or regulation of
the SEC that may at any time permit the investors to sell securities of the
Company to the public without registration ("RULE 144"), the Company agrees to:

                  (a) make and keep public information available, as those terms
         are understood and defined in Rule 144;

                  (b) file with the SEC in a timely manner all reports and other
         documents required of the Company under the 1933 Act and the 1934 Act
         so long as the Company remains subject to such requirements and the
         filing of such reports and other documents is required for the
         applicable provisions of Rule 144; and

                  (c) furnish to each Investor so long as such Investor owns
         Registrable Securities, promptly upon request, (i) a written statement
         by the Company that it has complied with the reporting requirements of
         Rule 144, the 1933 Act, and the 1934 Act, (ii) a copy of the most
         recent annual or quarterly report of the Company and such other reports
         and documents so filed by the Company, and (iii) such other information
         as may be reasonably requested to permit the investors to sell such
         securities pursuant to Rule 144 without registration.


         SECTION 9. ASSIGNMENT OF REGISTRATION RIGHTS.

         The rights to have the Company register Registrable Securities pursuant
to this Agreement shall be automatically assignable by the Investors to any
permitted transferee of all or any portion of Registrable Securities according
to the provisions of the Purchase Agreements and the Stock Option Agreements if:
(i) the Investor agrees in writing with the transferee or assignee to assign
such rights, and a copy of such agreement is furnished to the Company within a
reasonable time after such assignment; (ii) the Company is, within a reasonable
time after such transfer or assignment, furnished with written notice of (A) the
name and

<PAGE>   13


address of such transferee or assignee, and (B) the securities with respect to
which such registration rights are being transferred or assigned; (iii)
immediately following such transfer or assignment the further disposition of
such securities by the transferee or assignee is restricted under the 1933 Act
and applicable state securities laws; (iv) at or before the time the Company
receives the written notice contemplated by clause (ii) of this sentence the
transferee or assignee agrees in writing with the Company to be bound by all of
the provisions contained herein; (v) such transfer shall have been made in
accordance with the applicable requirements of the Purchase Agreements; (vi)
such transferee shall be an "accredited investor" as that term is defined in
Rule 501 of Regulation D promulgated under the 1933 Act; and (vii) in the event
the assignment occurs subsequent to the date of effectiveness of the
Registration Statement(s) required to be filed pursuant to Section 2(a), the
transferee agrees to pay all reasonable expenses of amending or supplementing
such Registration Statement(s) to reflect such assignment.


         SECTION 10. AMENDMENT OF REGISTRATION RIGHTS.

         Provisions of this Agreement may be amended and the observance thereof
may be waived (either generally or in a particular instance and either
retroactively or prospectively), only with the written consent of the Company
and Investors who hold two-thirds of the Registrable Securities. Any amendment
or waiver effected in accordance with this Section 10 shall be binding upon each
Investor and the Company.


         SECTION 11. MISCELLANEOUS.

                  (a) A person or entity is deemed to be a holder of Registrable
         Securities whenever such person or entity owns of record such
         Registrable Securities. If the Company receives conflicting
         instructions, notices, or elections from two or more persons or
         entities with respect to the same Registrable Securities, the Company
         shall act upon the basis of instructions, notice, or election received
         from the registered owner of such Registrable Securities.

                  (b) Any notices, consents, waivers, or other communications
         required or permitted to be given under the terms of this Agreement
         must be in writing and will be deemed to have been delivered (i) upon
         receipt, when delivered personally; (ii) upon receipt, when sent by
         facsimile, provided a copy is mailed by U.S. certified mail, return
         receipt requested; (iii) three (3) days after being sent by U.S.
         certified mail, return receipt requested, or (iv) one (1) day after
         deposit with a nationally recognized overnight delivery service, in
         each case properly addressed to the party to receive the same. The
         addresses and facsimile numbers for such communications shall be:

                  If to the Company:         RENTECH, INC.
                                             1331 17th Street, Suite 720
                                             Denver, CO  80202

                  with a copy (which shall not constitute notice) to:

                                             Loren L. Mall, Esq.
                                             Brega & Winters, P.C.
                                             1700 Lincoln Street, Suite 2222
                                             Denver, CO  80203


<PAGE>   14


                           If to a Purchaser, to its address and facsimile
         number on the Schedule of Purchasers, with copies to such Purchaser's
         counsel as set forth on the Schedule of Purchasers. Each party shall
         provide five (5) days prior written notice to the other party of any
         change in address or facsimile number.

                  (c) Failure of any party to exercise any right or remedy under
         this Agreement or otherwise, delay by a party in exercising such right
         or remedy, shall not operate as a waiver thereof.

                  (d) This Agreement shall be governed by and interpreted in
         accordance with the laws of the State of Colorado without regard to the
         principles of conflict of laws. If any provision of this Agreement
         shall be invalid or unenforceable in any jurisdiction, such invalidity
         or unenforceability shall not affect the validity or enforceability of
         the remainder of this Agreement in that jurisdiction or the validity or
         enforceability of any provision of this Agreement in any other
         jurisdiction.

                  (e) This Agreement, the Purchase Agreements and the Option
         Agreements constitute the entire agreement among the parties hereto
         with respect to the subject matter hereof and thereof. There are no
         restrictions, promises, warranties, or undertakings, other than those
         set forth or referred to herein and therein. This Agreement supersedes
         all prior agreements and understandings among the parties hereto with
         respect to the subject matter hereof.

                  (f) Subject to the requirements of Section 9, this Agreement
         shall inure to the benefit and of and be binding upon the permitted
         successors and assigns of each of the parties hereto.

                  (g) The headings in this Agreement are for convenience of
         reference only and shall not limit or otherwise affect the meaning
         hereof.

                  (h) This Agreement may be executed in two or more identical
         counterparts, each of which shall be deemed an original but all of
         which shall constitute one and the same agreement. This Agreement, once
         executed by a party, may be delivered to the other party hereto by
         facsimile transmission of a copy of this Agreement bearing the
         signature of the party so delivering this Agreement.

                  (i) Each party shall do and perform, or cause to be done and
         performed, all such further acts and things, and shall execute and
         deliver all such other agreements, certificates, instruments, and
         documents, as the other party may reasonably request in order to carry
         out the intent and accomplish the purposes of this Agreement and the
         consummation of the transactions contemplated hereby.

                            [Signature Page Follows]

<PAGE>   15

         IN WITNESS WHEREOF, the parties have caused this Registration Rights
Agreement to be duly executed as of day and year first above written.

                                    COMPANY:

                                    RENTECH, INC.


                                    By:
                                       --------------------------------
                                         Dennis L. Yakobson, President

FOREST OIL CORPORATION              ANSCHUTZ INVESTMENT COMPANY


By:                                 By:
   ------------------------------      --------------------------------
         Authorized Agent                    Authorized Agent

Address:                            Address:
        -------------------------           ---------------------------

Telephone:                          Telephone:
          -----------------------             -------------------------

Facsimile:                          Facsimile:
          -----------------------             -------------------------