6-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

Report of Foreign Private Issuer

Pursuant to Rule 13a-16 or 15d-16

of the Securities Exchange Act of 1934

For the month of April 2015

Commission File Number: 1-15256

OI S.A.

(Exact Name as Specified in its Charter)

N/A

(Translation of registrant’s name into English)

Rua General Polidoro, No. 99, 5th floor/part – Botafogo

22280-001 Rio de Janeiro, RJ

Federative Republic of Brazil

(Address of principal executive offices)

(Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.)

Form 20-F:  x            Form 40-F:  ¨

(Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1)):

Yes:  ¨             No:  x

(Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7)):

Yes:  ¨             No:  x

(Indicate by check mark whether the registrant by furnishing the information contained in this Form, the Registrant is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.)

Yes:  ¨             No:  x

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b):             

EXHIBIT INDEX

Exhibit Number	Description of Document
1	Notice to the Market, dated April 22, 2015 (English translation).
2	Material Fact, dated April 22, 2015 (English translation).

SIGNATURES

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

Date: April 22, 2015

OI S.A.
By:	/s/ Flavio Nicolay Guimarães
	Name:	Flavio Nicolay Guimarães
	Title:	Chief Financial Officer and Investor Relations Officer

EX-1

EXHIBIT 1

Oi S.A.

CORPORATE TAXPAYERS’ REGISTRY (CNPJ/MF) No. 76.535.764/0001-43

BOARD OF TRADE (NIRE) No. 33 3 0029520-8

Publicly-Held Company

NOTICE TO THE MARKET

Oi Announces Changes to its Management

Oi S.A. (“Oi” - Bovespa: OIBR3, OIBR4; NYSE: OIBR and OIBR.C), pursuant to art. 157, paragraph 4, of Law No. 6,404/76 and Instruction No. 358/02 of the Brazilian Securities and Exchange Commission (Comissão de Valores Mobiliários – CVM), and in accordance with corporate governance best practices, informs its shareholders and the market in general, that during the meeting held on Monday, April 20, 2015, the Company’s Board of Directors approved a change to the management structure, thereby creating (i) the Office of Corporate Finance, responsible for the Finance, Investor Relations, M&A and Controllership departments; and (ii) the Office of Financial Administration, responsible for the Supply, Accounting, Financial Services, Property, Logistics, and International Operations departments.

Mr. Flavio Nicolay Guimarães was elected to the position of Chief Financial Officer and Investor Relations Officer, assuming responsibility for the Office of Corporate Finance.

Mr. Marco Norci Schroeder was elected to the position of Executive Officer, assuming responsibility for the Office of Financial Administration.

Mr. Guimarães, age 40, is a graduate in International Business from Faculdades Associadas de São Paulo, with a certificate from the Wharton School of the University of Pennsylvania. He has substantial experience in financial markets, and has had a career in both domestic and international business finances. Mr. Guimarães joined Oi in May 2010 in the Financial Development and Administration department, and was named Treasury Officer on November 1, 2013, a position he has held to this date.

Mr. Schroeder, age 50, is a graduate in Economics from Universidade Federal Rio Grande do Sul, with a certificate from the Harvard Business School and the Wharton School of the University of Pennsylvania. Mr Schroeder developed a career in telecommunications, and is currently an Executive Officer of PT Portugal.

Rio de Janeiro, April 22, 2015.

Oi S.A.

Investor Relations Office

EX-2

EXHIBIT 2

Oi S.A.

CORPORATE TAXPAYERS’ REGISTRY (CNPJ/MF) No. 76.535.764/0001-43

BOARD OF TRADE (NIRE) No. 33 3 0029520-8

Publicly-Held Company

MATERIAL FACT

Approval of the European Commission of the Acquisition by Altice Portugal, S.A. of all PT Portugal, SGPS, S.A. Shares Held by Oi S.A.

and

Non-Opposition of the Portuguese Insurance and Pension Fund Supervisory Authority to the Acquisition by Altice Portugal, S.A. of a Qualified Indirect Participation in the Share Capital of Previsão – Sociedade Gestora de Fundos de Pensões, S.A.

Oi S.A. (“Oi” – Bovespa: OIBR3, OIBR4; NYSE: OIBR and OIBR.C), pursuant to art. 157, paragraph 4, of Law No. 6,404/76 and Instruction No. 358/02 of the Brazilian Securities and Exchange Commission (Comissão de Valores Mobiliários – CVM), and in furtherance of the Material Facts issued on November 3 and 30, 2014, and on December 8 and 9, 2014, informs its shareholders and the market in general, that it was notified by Altice Portugal, S.A. in respect to the conditions precedent regarding:

1. the approval by the European Commission of the acquisition by Altice Portugal, S.A. of all issued shares of PT Portugal, SGPS, S.A. (“PT Portugal”) held by Oi; and

2. the non-opposition of the Portuguese Insurance and Pension Fund Supervisory Authority (Autoridade de Supervisão de Seguros e Fundos de Pensões) to Altice Portugal, S.A. holding of a qualified indirect participation equal to 82.05% of the share capital of Previsão – Sociedade Gestora de Fundos de Pensões, S.A.

According to the terms stated in the European Commission’s correspondence of April 20, 2015, to which Altice Portugal, S.A. refers in its notice, the approval of the European Commission is conditioned on the French group selling the assets that it currently owns in Portugal, namely Cabovisão and ONI.

Oi would like to reiterate that, as previously disclosed to the market, prior to the consummation of the sale of PT Portugal and as a condition precedent to its closing, a corporate reorganization, which is currently taking place, is required in order to delineate the operations to be transferred as well as to separate PT Portugal’s investments which will not be included in the sale, including the investments in Africatel GmbH & Co. KG and Timor Telecom S.A., as well as all or part of PT Portugal’s indebtedness.

The Company will keep its shareholders and the market in general informed of any relevant subsequent events related to the topics discussed in this Material Fact.

Rio de Janeiro, April 22, 2015.

Oi S.A.

Flavio Nicolay Guimarães

Chief Financial Officer and Investor Relations Officer