<PAGE>   1
                                                                     EXHIBIT 4.3



                          REGISTRATION RIGHTS AGREEMENT


         This REGISTRATION RIGHTS AGREEMENT (this Agreement), dated as of
___________________, 1999, is entered into by and among Rentech, Inc., a
Colorado corporation (the Company), First Union Securities, Inc., and the
individuals and entities listed on Exhibit A hereto (collectively, the
Shareholders);

                            Background Circumstances:

         A. The Company and each of the Stockholders have entered into a
Subscription Agreement (the Subscription Agreement) relating to the purchase by
Stockholders of an aggregate of 12,500,000 shares of Common Stock, par value
$.01 per share (Shares) and 3,125,000 warrants to purchase Common Stock in
Units, consisting of four shares and one redeemable stock purchase warrant
(Warrant) to purchase one share of Common Stock, at an exercise price of $1.20
per share.

         B. In order to induce the Stockholders to enter into the Subscription
Agreement, the Company has agreed to grant certain registration rights to the
Stockholders with respect to the Shares and Warrant Shares;

         C. In connection with the private placement of the Shares with the
Stockholders, the Company has granted to First Union Securities, Inc. a warrant
to purchase one share of Common Stock for each 50 Shares of Common Stock sold in
the offering of the Units (the First Union Securities, Inc. Warrant Shares) at
an exercise price of $.66 per share.

         D. The Company has agreed to grant certain registration rights to First
Union Securities, Inc. with respect to the First Union Securities, Inc. Warrant
Shares;

         NOW, THEREFORE, in consideration of the foregoing and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto hereby agree as follows:

1.       Definitions.

         As used herein, the following terms have the indicated meanings, unless
the context otherwise requires:

         "Act" means the Securities Act of 1933, as amended.

         "Commission" means the Securities and Exchange Commission.

         "Exchange Act" means the Securities Exchange Act of 1934, as amended.

         "Holder" means a Stockholder who owns Registrable Securities or any
permitted transferee thereof who owns Registrable Securities Rights under this
Agreement may not be exercised except by persons who purchased Units from
Rentech, Inc., each Unit consisting of four shares of Common Stock and one
Warrant for the purchase of one share of Common Stock, or persons to whom both
the shares and the Warrant comprising the Units have been transferred.

         "Registrable Securities" means the Shares, Warrant Shares, First Union
Securities, Inc. Warrant Shares and any other securities issued or issuable by
the Company with respect to the Shares, Warrant Shares or the First Union
Securities, Inc. Warrant Shares by way of a stock dividend or other distribution
or stock split or in connection with a combination of shares, recapitalization,
merger, consolidation or reorganization. Any Registrable Securities will cease
to be such when (i) a registration statement covering such Registrable
Securities has been declared effective by the Securities and Exchange Commission
and




<PAGE>   2


such Registrable Securities have been disposed of pursuant to such effective
registration statement, (ii) such Registrable Securities may be distributed to
the public pursuant to Rule 144 (or any similar provision then in force) under
the Act or (iii) the Company has delivered a new certificate or other evidence
of ownership for such Registrable Securities not bearing the legend required
pursuant to the Subscription Agreement or a Warrant to Purchase Common Stock
regarding the Warrant Shares or the First Union Securities, Inc. Warrant Shares
and such Registrable Securities may be resold to the public without restriction
under the Act in accordance with Rule 144(k).

         "Selling Holder" means a Stockholder or permitted transferee thereof
who is selling Registrable Securities pursuant to a registration statement.

2.       Piggy-Back Registration.

         (a) If the Company proposes to file a registration statement under the
Act with respect to an offering by the Company of any class of equity security
for cash, including any security convertible into or exchangeable for any equity
securities (other than (i) a registration statement on Form S-4 or S-8 (or any
substitute form for comparable purposes that may be adopted by the Commission),
(ii) a registration statement filed in connection with an exchange offer or an
offering of securities solely to the Company's existing security holders, or
(iii) in connection with the registration statement that is on a form pursuant
to which an offering of the Registrable Securities cannot be registered, then
the Company shall in each case give written notice of such proposed filing to
the Holders at least 30 days before the anticipated filing date, and such notice
shall offer the Holders the opportunity to register such number of Registrable
Securities as each such Holder may request. Upon the written request of any
Holder received by the Company within 15 business days after the date of the
Company's delivery of its notice to the Holders of its intention to file such a
registration statement, the Company shall, subject to the conditions and in
accordance with the procedures set forth herein, use its best efforts to cause
the managing underwriter or underwriters, if any, of a proposed underwritten
offering to permit the Registrable Securities requested by the Holder to be
included in the registration statement for such offering on the same terms and
conditions as any similar securities of the Company included therein (a
"Piggy-Back Registration"). Notwithstanding the foregoing, if the managing
underwriter or underwriters of an offering indicates in writing to the Holders
who have requested that their Registrable Shares be included in such offering,
its reasonable belief that because of the size of the offering intended to be
made, the inclusion of the Registrable Securities requested to be included might
reasonably be expected to jeopardize the success of the offering of the
securities of the Company to be offered and sold by the Company for its own
account, then the amount of securities to be offered for the account of the
Holders shall be reduced on a pro rata basis among the selling Holders
(according to he total amount of securities owned by selling Holders) other than
the Company to the extent necessary to reduce the total amount of securities to
be included in such offering to the amount recommended by such managing
underwriter or underwriters. The Company will bear all Registration Expenses (as
hereinafter defined) in connection with a Piggy-Back Registration.

         (b) The Company may, without the consent of any Selling Holder,
withdraw any registration statement prior to the effectiveness thereof and
abandon any proposed offering initiated by the Company, notwithstanding the
request of a Holder to participate therein in accordance with this Section 2, if
the Company determines that such action is in the best interests of the Company.

         (c) Notwithstanding anything contained herein to the contrary, the
Company will have no obligation under this Section 2 to register any Registrable
Securities unless at least 20,000 shares (as adjusted for stock splits, stock
dividends or similar transaction) of Registrable Securities in the aggregate are
requested to be included in such offering.

3.       Restrictions on Public Sale by Holder of Registrable Securities.

         To the extent not inconsistent with applicable law, each Holder whose
Registrable Securities are included in a registration statement pursuant to
Section 2 agrees not to effect any public sale or



                                        2
<PAGE>   3



distribution of the security being registered or a similar security of the
Company, or any securities convertible into or exchangeable or exercisable for
such securities, including a sale pursuant to Rule 144 under the Act, during the
90-day period (or such shorter period as may be required by the Company or the
managing underwriter or underwriters with respect to any officer or director or
shareholder of the Company) beginning on the effective date of a registration
statement (except, in each case, as part of such registration), if and to the
extent requested by the Company in the case of a non-underwritten public
offering or if and to the extent requested by the managing underwriter or
underwriters in the case of an underwritten public offering.

4.       Registration Procedures.

         Whenever the Holders have requested that any Registrable Securities be
included in a registration pursuant to Section 2 hereof, the Company shall
(unless such registration statement is not filed or is withdrawn) use its best
efforts to effect the registration and the sale of such Registrable Securities
as soon as reasonably practicable, and in connection with any such request, the
Company shall (unless such registration statement is not filed or is withdrawn):

         (a) (I) prior to filing a registration statement or prospectus or any
amendments or supplements thereto, furnish to each Selling Holder and counsel
selected by each Selling Holder copies of all such documents proposed to be
filed, which documents will be subject to the review of such counsel, (ii)
furnish to each Selling Holder, prior to filing a registration statement, copies
of such registration statement as proposed to be filed, and thereafter furnish
to each Selling Holder such number of copies of such registration statement,
each amendment and supplement thereto (in each case including all exhibits
thereto), the prospectus included in such registration statement (including each
preliminary prospectus) and such other documents as any Selling Holder may
reasonably require in order to facilitate the disposition of the Registrable
Securities owned by the Selling Holder, and (iii) after the filing of the
registration statement, promptly notify each Selling Holder of Registrable
Securities covered by such registration statement of any stop order issued or
threatened by the Commission and take all reasonable actions required to prevent
the entry of such stop order or to remove it if entered;

         (b) use its best efforts to register or qualify such Registrable
Securities under such other securities or blue sky laws of such jurisdictions as
each Selling Holder reasonably requests and do any and all other acts and things
which may be reasonably necessary or advisable to enable the Selling Holder to
consummate the disposition in such jurisdictions of the Registrable Securities
owned by the Selling Holder; provided, however, that the Company will not be
required to (I) qualify generally to do business in any jurisdiction where it
would not otherwise be required to qualify but for this paragraph (b), (ii)
subject itself to taxation in any such jurisdiction where it is not then so
subject or (iii) consent to general service of process in any such jurisdiction;

         (c) use its best efforts to cause such Registrable Securities to be
registered with or approved by such other governmental agencies or authorities
as may be necessary by virtue of the business and operations of the Company to
enable the Selling Holder thereof to consummate the disposition of such
Registrable Securities;

         (d) notify the Selling Holder, at any time when a prospectus relating
thereto is required to be delivered under the Act, of the occurrence of an event
requiring the preparation of a supplement or amendment to such prospectus so
that, as thereafter delivered to the purchasers of such Registrable Securities,
such prospectus will not contain an untrue statement of a material fact or omit
to state any material fact required to be stated therein or necessary to make
the statements therein not misleading and promptly make available to the Selling
Holder any such supplement or amendment;

         (e) enter into or arrange for the furnishing of customary agreements
and documents (including an underwriting agreement in customary form) and take
such other actions as are reasonably required in order to expedite or facilitate
the disposition of such Registrable Securities;


                                       3
<PAGE>   4


         (f) make available for inspection by each Selling Holder, any
underwriter participating in any disposition pursuant to such registration
statement and any attorney, accountant or other professional retained by the
Selling Holder or underwriter (collectively, the Inspectors), all financial and
other records, pertinent corporate documents and properties of the Company and
its subsidiaries (collectively, the Records) as shall be reasonably necessary to
enable them to exercise their due diligence responsibility, and cause the
Company's and its subsidiaries' officers, directors and employees to supply all
information reasonably requested by any such Inspector in connection with such
registration statement. Each Selling Holder agrees that information obtained by
it as a result of such inspections that is material and deemed confidential
shall not be used by it as the basis for any market transactions in securities
of the Company unless and until such is made generally available to the public.
The Selling Holder further agrees that it will, upon learning that disclosure of
such Records is sought in a court of competent jurisdiction, give notice to the
Company and allow the Company, at the Company's expense, to undertake
appropriate action to prevent disclosure of the Records deemed confidential;

         (g) otherwise comply with all applicable rules and regulations of the
Commission, and make available to its security holders, as soon as reasonably
practicable, an earnings statement covering a period of 12 months, beginning
within three months after the effective date of the registration statement,
which earnings statement shall satisfy the provisions of Section 11(a) of the
Act; and

         (h) use its reasonable efforts to cause all such Registrable Securities
to be quoted on the Nasdaq Market System, if the Common Stock is then so quoted,
or to be listed on any securities exchange on which the Common Stock is then
listed.

         The Company may require the Selling Holder as to which any registration
is being effected to furnish to the Company such information regarding the
Selling Holder and the distribution of such Registrable Securities as the
Company may from time to time reasonably request in writing and such other
information as may be legally required in connection with such registration.

         In no event shall the Company be required to amend any registration
statement filed pursuant to this Agreement after it has become effective or to
amend or supplement any prospectus to permit the continued disposition of shares
of Common Stock owned by a Selling Holder registered under any such registration
statement beyond the period during which the Company is required to maintain the
effectiveness thereof pursuant to the terms of this Agreement.

         Each Selling Holder agrees that, upon receipt of any notice from the
Company of the happening of any event of the kind described in Section 4(d)
hereof, the Selling Holder will forthwith discontinue disposition of Registrable
Securities pursuant to the registration statement covering such Registrable
Securities until the Selling Holder's receipt of the copies of the supplemented
or amended prospectus contemplated by Section 4(d) hereof, and, if so directed
by the Company, the Selling Holder will deliver to the Company (at the Company's
expense) all copies, other than permanent file copies then in the Selling
Holder's possession, of the prospectus covering such Registrable Securities
current at the time of receipt of such notice. Each Selling Holder also agrees
to notify the Company of any event relating to the Selling Holder that occurs
that would require the preparation of a supplement or amendment to the
prospectus so that such prospectus will not contain an 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 not misleading.

         As used herein, the term "Current Market Price" per share of Common
Stock or any other security at any date shall mean, on any date of determination
(a) the average of the daily closing sale price for the 10 trading days
immediately preceding such date if the security has been listed on the New York
Stock Exchange, the American Stock Exchange or other national exchange or the
Nasdaq National Market for at least 10 trading days prior to such date, (b) if
such security is not so listed or traded, the average of the daily closing bid
price for the 10 trading days immediately preceding such date if the security
has been quoted on a national over-the-counter market for at least 10 trading
days, and (c) otherwise, the value of the security most recently determined as
of a date within the six months preceding such day by the Company's Board of
Directors.


                                       4
<PAGE>   5


5.       Registration Expenses.

         All expenses incident to the Company's performance of or compliance
with this Agreement, including, without limitation, all registration and filing
fees, fees and expenses of compliance with securities or blue sky laws
(including fees and disbursements of counsel in connection with blue sky
qualifications of the Registrable Securities), rating agency fees, printing
expenses, messenger and delivery expenses, internal expenses (including, without
limitation, all salaries and expenses of its officers and employees performing
legal or accounting duties), the fees and expenses incurred in connection with
the listing of the securities to be registered on the Nasdaq Market System and
all securities exchanges on which similar securities issued by the Company are
then quoted or listed, and fees and disbursements of counsel for the Company and
its independent certified public accountants (including the expenses of any
special audit or comfort letters required by or incident to such performance),
securities act liability insurance (if the Company elects to obtain such
insurance), the fees and expenses of any special experts retained by the Company
in connection with such registration, and fees and expenses of other persons
retained by the Company, in connection with each registration hereunder (but not
including any underwriting discounts or commissions attributable to the sale of
Registrable Securities (which are hereinafter referred to as "Selling Expenses")
and the reasonable fees and expenses of one counsel for the Selling Holders,
(collectively, the "Registration Expenses") will be borne by the Company in the
event of a registration of Registrable Securities pursuant to Section 2 or 3
hereof. All Selling Expenses shall be borne solely by the Selling Holders.

6.       Indemnification; Contribution.

         (a) Indemnification by the Company. To the extent permitted by
applicable law, the Company agrees to indemnify and hold harmless each Selling
Holder, its officers, directors, partners and agents and each person, if any,
who controls a Selling Holder within the meaning of Section 15 of the Act or
Section 20 of the Exchange Act, from and against any and all losses, claims,
damages (whether in contract, tort or otherwise), liabilities and expenses
(including reasonable costs of investigation) whatsoever (as incurred or
suffered) arising out of or based upon any untrue statement or alleged untrue
statement of a material fact contained in any registration statement or
prospectus relating to the Registrable Securities or in any amendment or
supplement thereto or in any preliminary prospectus, or arising out of or based
upon any omission or alleged omission to state therein a material fact required
to be stated therein or necessary to make the statements therein not misleading,
except insofar as such losses, claims, damages, liabilities or expenses arise
out of, or are based upon, any such untrue statement or omission or allegation
thereof based upon information furnished in writing to the Company by such
Selling Holder or on behalf of such Selling Holder expressly for use therein and
provided, that with respect to any untrue statement or omission or alleged
untrue statement or omission made in any preliminary prospectus, the indemnity
agreement contained in this paragraph shall not apply to the extent that any
such loss, claim, damage, liability or expense results from the fact that a
current copy of the prospectus was not sent or given to the person asserting any
such loss, claim, damage, liability or expense at or prior to the written
confirmation of the sale of the Registrable Securities concerned to such person
if it is determined that the Company had previously provided such Selling Holder
with such current copy of the prospectus, it was the responsibility of such
Selling Holder to provide such person with such current copy of the prospectus
and such current copy of the prospectus would have cured the defect giving rise
to such loss, claim, damage, liability or expense. The Company also agrees to
indemnify any underwriters of the Registrable Securities, their officers,
partners and directors and each person who controls such underwriters on
substantially the same basis as that of the indemnification of the Selling
Holder provided in this Section 7 or such other indemnification customarily
obtained by underwriters at the time of offering.

         (b) Conduct of Indemnification Proceedings. If any action or proceeding
(including any governmental investigation) shall be brought or asserted against
a Selling Holder (or its officers, directors, partners, attorneys or agents) or
any person controlling such Selling Holder in respect of which indemnity may be
sought from the Company, the Company shall assume the defense thereof, including
the employment of counsel reasonably satisfactory to such Selling Holder, and
shall assume the payment of all expenses. Each Selling Holder or any controlling
person of a Selling Holder shall have the right to


                                       5
<PAGE>   6


employ separate counsel in any such action and to participate in the defense
thereof, but the fees and expenses of such counsel shall be at the expense of
such Selling Holder or such controlling person unless (I) the Company has agreed
to pay such fees and expenses or (ii) the named parties to any such action or
proceeding (including any impleaded parties) include both the Selling Holder or
such controlling person and the Company, and the Selling Holder or such
controlling person shall have been advised by counsel that there may be one or
more legal defenses available to such Selling Holder or such controlling person
which are different from or additional to those available to the Company (in
which case, if such Selling Holder or such controlling person notifies the
Company in writing that it elects to employ separate counsel at the expense of
the Company, the Company shall not have the right to assume the defense of such
action or proceeding on behalf of such Selling Holder or such controlling
person) or (iii) the use of counsel chosen by the Company to represent the
Selling Holder would present such counsel with a conflict of interest or (iv)
the Company shall not have employed counsel satisfactory to the Selling Holder
to represent the Selling Holder within a reasonable time after notice of the
institution of such action; it being understood, however, that the Company shall
not, in connection with any one such action or proceeding or separate but
substantially similar or related actions or proceedings in the same jurisdiction
arising out of the same general allegations or circumstances, be liable for the
fees and expenses of more than one separate firm of attorneys (together with
appropriate local counsel) at any time for each Selling Holder, which firm shall
be designated in writing by such Selling Holder). The Company shall not be
liable for any settlement of any such action or proceeding effected without the
Company's written consent, but if settled with its written consent, or if there
be a final judgment for the plaintiff in any such action or proceeding, the
Company agrees to indemnify and hold harmless each Selling Holder and
controlling person from and against any loss or liability (to the extent stated
above) by reason of such settlement or judgment. The Company shall not, without
the prior written consent of the Selling Holder, settle or compromise or consent
to the entry of any judgment with respect to any pending or threatened claim,
action, suit or proceeding in respect of which indemnification or contribution
may be sought hereunder (whether or not the Selling Holders are actual or
potential parties to such claim or action) unless such settlement, compromise or
consent includes an unconditional release of each Selling Holder from all
liability arising out of such claim, action, suit or proceeding.

         (c) Indemnification by Holder of Registrable Securities. Each Selling
Holder agrees to indemnify and hold harmless the Company, its directors and
officers and each person, if any, who controls the Company within the meaning of
either Section 15 of the Act or Section 20 of the Exchange Act, to the same
extent as the foregoing indemnity from the Company to the Selling Holder, but
only with respect to information furnished in writing by the Selling Holder or
on the Selling Holder's behalf expressly for use in any registration statement
or prospectus relating to the Registrable Securities, or any amendment or
supplement thereto, or any preliminary prospectus. In case any action or
proceeding shall be brought against the Company or its directors or officers, or
any such controlling person, in respect of which indemnity may be sought against
a Selling Holder, such Selling Holder shall have the rights and duties given to
the Company, and the Company or its directors or officers or such controlling
person shall have the rights and duties given to a Selling Holder, by the
preceding paragraph. The Selling Holder also agrees that it will enter into an
indemnity agreement to indemnify and hold harmless underwriters of the
Registrable Securities, their officers and directors and each person who
controls such underwriters on substantially the same basis as that of the
indemnification of the Company provided in this Section 7(c). Notwithstanding
the foregoing, the liability of a Selling Holder pursuant to this Section 7(c)
shall not exceed the amount of the aggregate proceeds of the Registrable
Securities of the Selling Holder.

         (d) Contribution. If the indemnification provided for in this Section 7
is unavailable to the Company or a Selling Holder in respect of any losses,
claims, damages, liabilities or judgments referred to herein, then each such
indemnifying party, in lieu of indemnifying such indemnified party, shall
contribute to the amount paid or payable by such indemnified party as a result
of such losses, claims, damages, liabilities and judgments (I) as between the
Company and such Selling Holder on the one hand and the underwriters on the
other, in such proportion as is appropriate to reflect the relative benefits
received by the Company and a Selling Holder on the one hand and the
underwriters on the other from the offering of the Registrable Securities, or if
such allocation is not permitted by applicable law, in such proportion as is
appropriate to reflect not only such relative benefits but also the relative
fault of the



                                       6
<PAGE>   7


Company and such Selling Holder on the one hand and of the underwriters on the
other in connection with the statements or omissions which resulted in such
losses, claims, damages, liabilities or judgments, as well as any other relevant
equitable considerations and (ii) as between the Company, on the one hand, and a
Selling Holder on the other, in such proportion as is appropriate to reflect the
relative fault of the Company and of such Selling Holder in connection with such
statements or omissions, as well as any other relevant equitable considerations.
The relative benefits received by the Company and a Selling Holder on the one
hand and the underwriters on the other shall be deemed to be in the same
proportion as the total proceeds from the offering (net of underwriting
discounts and commissions but before deducting expenses) received by the Company
and such Selling Holder bear to the total underwriting discounts and commissions
received by the underwriters, in each case as set forth in the table on the
cover page of the prospectus. The relative fault of the Company and such Selling
Holder on the one hand and of the underwriters on the other shall be determined
by reference to, among other things, whether the untrue or alleged untrue
statement of a material fact or the omission or alleged omission to state a
material fact relates to information supplied by the Company and such Selling
Holder or by the underwriters. The relative fault of the Company on the one hand
and of such Selling Holder on the other shall be determined by reference to,
among other things, whether the untrue or alleged untrue statement of a material
fact or the omission or alleged omission to state a material fact relates to
information supplied by such party, and the parties' relative intent, knowledge,
access to information and opportunity to correct or prevent such statement or
omission.

         The Company and each Selling Holder agree that it would not be just and
equitable if contribution pursuant to this Section 6(d) were determined by pro
rata allocation (even if the underwriters were treated as one entity for such
purpose) or by any other method of allocation which does not take account of the
equitable considerations referred to in the immediately preceding paragraph. The
amount paid or payable by an indemnified party as a result of the losses,
claims, damages, liabilities, or judgments referred to in the immediately
preceding paragraph shall be deemed to include, subject to the limitations set
forth above, any legal or other expenses reasonably incurred by such indemnified
party in connection with investigating or defending any such action or claim.
Notwithstanding the provisions of this Section 6(d), no underwriter shall be
required to contribute any amount in excess of the amount by which the total
price at which the Registrable Securities underwritten by it and distributed to
the public were offered to the public exceeds the amount of any damages which
such underwriter has otherwise been required to pay by reason of such untrue or
alleged untrue statement or omission or alleged omission, and a Selling Holder
shall not be required to contribute any amount in excess of the amount of the
total price at which the Registrable Securities of the Selling Holder were
offered to the public. No person guilty of fraudulent misrepresentation (within
the meaning of Section 11(f) of the Act) shall be entitled to contribution from
any person who was not guilty of such fraudulent misrepresentation.

         (e) Indemnification Payments. The indemnification and contribution
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 expense, loss, damage or liability are incurred.

7.       Participation in Underwritten Registrations.

         No person may participate in any underwritten registration hereunder
unless such person (a) agrees to sell such person's securities on the basis
provided in any underwriting arrangements approved by the persons entitled
hereunder to approve such arrangements and (b) completes and executes all
questionnaires, powers of attorney, custody agreements, indemnities,
underwriting agreements and other documents reasonably required by the Company
or managing underwriter under the terms of such underwriting arrangements and
this Agreement.


                                       7
<PAGE>   8


8.       Rule 144 and Reports.

         The Company shall timely file the reports required to be filed by it
under the Securities Act and the Exchange Act (including but not limited to the
reports under Sections 13 and 15(d) of the Exchange Act referred to in
subparagraph (c)(1) of Rule 144 adopted by the Commission under the Securities
Act) and the rules and regulations adopted by the Commission thereunder (or, if
the Company is not required to file such reports, will, upon the request of any
holder of Registrable Securities, make publicly available other information) and
will take such further action as any holder of Registrable Securities may
reasonably request, all to the extent required from time to time to enable such
holder to sell Registrable Securities without registration under the Securities
Act within the limitation of the exemptions provided by (a) Rule 144 under the
Securities Act, as such Rule may be amended from time to time, or (b) any
similar rule of regulation hereafter adopted by the Commission. Upon the request
of any holder of Registrable Securities, the Company will deliver to such holder
a written statement as to whether it has complied with such requirements.

9.       Miscellaneous.

         (a) Binding Effect. Unless otherwise provided herein, the provisions of
this Agreement shall be binding upon and accrue to the benefit of the parties
hereto and their respective heirs and legal representatives and permitted
transferees, successors and assigns. The rights and obligations of a Holder
hereunder cannot be assigned or transferred without the prior written consent of
the Company except by will or intestacy or by operation of law.

         (b) Amendment. This Agreement may be amended or terminated only by a
written instrument signed by the Company and each of the Holders.

         (c) Applicable Law. The internal laws of the State of New York (without
regard to choice of law provisions thereof) shall govern the interpretation,
validity and performance of the terms of this Agreement.

         (d) Notices. All notices provided for herein shall be in writing and
shall be deemed to have been duly given if delivered personally or sent by
registered or certified mail, postage prepaid:



<TABLE>

         <S>      <C>                                         <C>
         (I)      if to the Company, to:                      With a copy to:

                  Rentech, Inc.                                        Brega & Winters P.C.
                  1331 17th Street, Suite 720                          1700 Lincoln St., #2222
                  Denver, CO 80202                                     Denver, CO 80203
                  Attention:  President                                Attn:  Mr. Loren Mall

         (ii)     if to First Union Securities, Inc.:                  With a copy to:

                  First Union Securities                      Vinson & Elkins L.L.P.
                  1001 Fannin, 22nd Floor                              2300 First City Tower
                  Houston, TX  77002-6760                              1001 Fannin
                  Attn:  Mr. John Bishop                      Houston, TX 77002-6760
                                                                       Attention:  Mr. T. Mark Kelly

         (iii)    if to the Stockholders, to the respective addresses
                  set forth on Exhibit A hereto.
</TABLE>

         (e) Counterparts. This Agreement may be executed in one or more
counterparts, each of which shall be deemed to be an original and all of which
together shall be deemed to be one instrument.



                                       8
<PAGE>   9


         (f) Severability. If any term, provision, covenant or restriction of
this Agreement is held by a court of competent jurisdiction to be invalid, void
or unenforceable, the remainder of the terms, provisions, covenants, and
restrictions of this Agreement shall remain in full force and effect.

         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed as of the date first above written.

                                       RENTECH, INC.


                                       By:
                                            ------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------


                                       FIRST UNION SECURITIES, INC.


                                       By:
                                            ------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------

                                       STOCKHOLDERS:

                                       -----------------------------------------




                                       9