May 21, 2006 — On Friday, May 19, Mittal Steel Co. NV announced it would improve its offer made to the security holders of Arcelor SA.

Based on the Mittal Steel share closing price, on the NYSE, on May 18, 2006, the revised offer values each Arcelor share at EUR37.74, which represents a 33.8% premium over the consideration offered in the offer announced by Mittal Steel on January 27, 2006, a 17.9% premium over the closing price on Euronext Paris of Arcelor shares on May 18, 2006, and a 69.8% premium over the closing price on Euronext Paris of Arcelor shares on January 26, 2006. Based on the average closing price, on the NYSE, of Mittal Steel shares over the 30 calendar days prior to 19th May 2006, the revised offer values each Arcelor share at EUR41.5.

This offer values Arcelor at an equity value of EUR25.8 billion on a fully diluted basis.

Under terms of the revised offer, Arcelor shareholders will receive one (1) Mittal Steel share and EUR11.10 cash for each Arcelor share, to be adjusted as provided in the terms and conditions of the current offer (including all distributions in excess of EUR0.8 per share). Arcelor shareholders may opt for a cash or stock mix in any proportion they elect, provided that overall 29.4% of the aggregate consideration paid to Arcelor shareholders is paid in cash and 70.6% in stock. The maximum amount of cash to be paid by Mittal Steel will be approximately EUR7.6 billion and the maximum number of Mittal Steel shares to be issued will be approximately 684.46 million.

Mittal Steel also announces significant changes to its corporate governance, including the adoption of a one-share one-vote structure.

Mittal Steel expects to formally file the documentation relating to its revised offer, with the AFM, the CSSF, the CBFA, the AMF, the CNMV and the SEC shortly.

Mr. Lakshmi N. Mittal, Chairman and CEO of Mittal Steel said, "We have today announced a materially improved offer, providing an exceptionally attractive premium to Arcelor shareholders. Not only are we offering a very significant increase in the cash component, but also a greater participation in the combined company.

"The revision reflects our long-term confidence in the health and prospects of the steel industry, in which the Arcelor/Mittal combination would be the undisputed sector leader."

HIGHLIGHTS OF THE REVISED TERMS OF THE OFFER

Revised Terms and Conditions of the Offer—Subject to the terms and conditions set forth in the current Offer Document, Mittal Steel will be offering to acquire all outstanding Arcelor ordinary shares and Arcelor Convertible Bonds (2017 OCEANEs), as follows:

• One (1) new Mittal Steel share and EUR11.10 in cash for each Arcelor ordinary shares (the amount of cash being reduced to EUR10.05 upon payment by Arcelor of the announced EUR1.85 dividend);
• One (1) new Mittal Steel shares and EUR12.12 in cash (to be increased by EUR0.80 upon distribution by Arcelor of its announced ordinary dividend) for each Arcelor Convertible Bond.

Holders of Arcelor shares may, in lieu of this mix of Mittal Steel stock and cash, make the following elections with respect to the consideration to be received:

• Elect to receive seventeen (17) new Mittal Steel shares for every twelve (12) Arcelor shares (such ratio shall become 1.3773 new Mittal Steel share for each Arcelor share upon payment by Arcelor of the announced EUR1.85 dividend); or
• Elect to receive EUR37.74 in cash for each Arcelor share (the amount of cash being reduced to EUR36.69 upon payment by Arcelor of the announced EUR1.85 dividend).

Holders will not be required to make the same election for all Arcelor shares tendered, and either of these elections may be made for all or some of the Arcelor shares to be tendered. However, these elections will be subject to a proration and allocation procedure that will ensure that 70.6% of the tendered Arcelor shares are exchanged for new Mittal Steel shares and 29.4% are exchanged for cash.

If certain actions are taken by Arcelor including distributions or share buy-backs or issuance of new shares, the consideration set forth above and the overall amount of cash available in the revised offer will be adjusted accordingly, in accordance with the same rules as detailed in the current Offer Document.

All other terms and conditions set forth in the current Offer Document will apply to the revised offer and remain unchanged, subject to the corporate governance changes set forth below.

Corporate Governance Modifications—Upon completion of the offer, Mittal Steel intends to modify its corporate governance. As part of the revision, Mittal Steel will amend its articles of association so as to eliminate all differences between class A common shares and class B common shares. All shareholders will hold ordinary shares carrying the same voting and economic rights. Each share will have one vote, irrespective of the length of time it has been held. The current right of holders of Mittal Steel class B common shares to make binding nominations for appointments to Mittal Steel's Board of Directors will be removed. Directors will be elected by the general meeting of the shareholders, by a simple majority of the votes cast.

Mittal Steel says it will also propose to enlarge the Board of Directors of Mittal Steel to 14 members. The Board of Directors will have a majority of independent directors. Mittal Steel also plans to simplify the term of office for Directors such that all directors would be elected by the general meeting of shareholders for a term of office of three years. Currently, both Mittal Steel and Arcelor directors are elected for a term of office that varies from one to five years.

Mittal Steel also says that it plans to have a management team reflecting the best talent for each position. The new organizational structure will be developed with senior management of both companies. Further, the company's global headquarters and domicile will be relocated to Luxembourg.

After completion of the revised offer, assuming that all Arcelor shares have been tendered, the Mittal family stake in the combined entity will be around 45% in share capital and voting rights.

Mittal Steel says that it intends to share elements of its business plan with Arcelor shortly. If Mittal Steel's revised offer is recommended by the Board of Directors of Arcelor, the proposals made with respect to the composition of the Board of Directors and Management Board will be maintained.

Mittal Steel Co. has operations in sixteen countries, on four continents. Mittal Steel encompasses all aspects of modern steelmaking, to produce a comprehensive portfolio of both flat and long steel products to meet a wide range of customer needs. It serves all the major steel consuming sectors, including automotive, appliance, machinery and construction. For 2005, Mittal Steel had revenues of US$28.1 billion and steel shipments of 49.2 million tons.