<PAGE>
                                                                     EXHIBIT 4.3

                             [FORM OF SERIES B NOTE]


                               NRP (OPERATING) LLC


                 4.91% SENIOR NOTE, SERIES B, DUE JUNE 19, 2018

No. [_________]                                                           [Date]
$[____________]                                                  PPN 62963# AB 7

         FOR VALUE RECEIVED, the undersigned, NRP (OPERATING) LLC (herein called
the "Company"), a limited liability company organized and existing under the
laws of the State of Delaware, hereby promises to pay to [________________], or
registered assigns, the principal sum of [________________] DOLLARS on June 19,
2018 with interest (computed on the basis of a 360-day year of twelve 30-day
months) (a) on the unpaid balance thereof at the rate of 4.91% per annum from
the date hereof, payable semiannually, on the 19th day of June and December in
each year, commencing with the June or December next succeeding the date hereof,
until the principal hereof shall have become due and payable, and (b) to the
extent permitted by law on any overdue payment (including any overdue
prepayment) of principal, any overdue payment of interest and any overdue
payment of any Make-Whole Amount (as defined in the Note Purchase Agreements
referred to below), payable semiannually as aforesaid (or, at the option of the
registered holder hereof, on demand), at a rate per annum from time to time
equal to the greater of (i) 2.00% plus coupon or (ii) 2% over the rate of
interest publicly announced by Citibank, N.A. from time to time in New York, New
York as its "base" or "prime" rate.

         Payments of principal of, interest on and any Make-Whole Amount with
respect to this Note are to be made in lawful money of the United States of
America at Citibank, N.A. or at such other place as the Company shall have
designated by written notice to the holder of this Note as provided in the Note
Purchase Agreements referred to below.

         This Note is one of the Series B Senior Notes (herein called the
"Series B Notes") issued pursuant to separate Note Purchase Agreements, dated as
of June 19, 2003 (as from time to time amended and supplemented, the "Note
Purchase Agreements"), between the Company and the respective Purchasers named
therein and is entitled to the benefits thereof. Each holder of this Note will
be deemed, by its acceptance hereof, (i) to have agreed to the confidentiality
provisions set forth in Section 20 of the Note Purchase Agreements and (ii) to
have made the representation set forth in Section 6.2 of the Note Purchase
Agreements.

         This Series B Note is a registered Series B Note and, as provided in
the Note Purchase Agreements, upon surrender of this Series B Note for
registration of transfer, duly endorsed, or accompanied by a written instrument
of transfer duly executed, by the registered holder hereof or such holder's
attorney duly authorized in writing, a new Series B Note for a like principal
amount will be issued to, and registered in the name of,



<PAGE>


the transferee. Prior to due presentment for registration of transfer, the
Company may treat the person in whose name this Series B Note is registered as
the owner hereof for the purpose of receiving payment and for all other
purposes, and the Company will not be affected by any notice to the contrary.

         The Company will make required prepayments of principal on the dates
and in the amounts specified in the Note Purchase Agreements. This Series B Note
is also subject to optional prepayment, in whole or from time to time in part,
at the times and on the terms specified in the Note Purchase Agreements, but not
otherwise.

         If an Event of Default, as defined in the Note Purchase Agreements,
occurs and is continuing, the principal of this Series B Note may be declared or
otherwise become due and payable in the manner, at the price (including any
applicable Make-Whole Amount) and with the effect provided in the Note Purchase
Agreements.

         This Series B Note is guaranteed pursuant to the Subsidiary Guarantee
dated June 19, 2003.

         This Series B Note shall be construed and enforced in accordance with,
and the rights of the parties shall be governed by, the law of the State of New
York excluding choice-of-law principles of law of such State that would require
the application of the laws of a jurisdiction other than such State.



                                     NRP (OPERATING) LLC, a Delaware
                                       limited liability company




                                     By _______________________________________
                                        [Name]
                                        [Title]