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Exhibit 12.1

Chief Executive Officer Certification 
Pursuant to Section 302 of the Sarbanes-Oxley Act of 2002

I, Felipe Cerón, Chief Executive Officer of AES Gener S.A., certify that:

|1. | I have reviewed this annual report on Form 20-F of AES Gener S.A.;                                                                                                                                                                                                                                        
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|2. | Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading
with respect to the period covered by this report;
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|3. | Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the company as of, and for, the
periods presented in this report;                      
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|4. | The company's other certifying officers and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the company and have:                                                                                    
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|   | a)                                                                                                                                                                                                                                                                                                        
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|   | b)                                                                                                                                                                                                                                                                                                        
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|   | c)                                                                                                                                                                                                                                                                                                        
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|5. | The company's other certifying officers and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the company's auditors and the audit committee of the company's board of directors (or persons
performing the equivalent functions):                   
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|   | a)                                                                                                                                                                                                                                                                                                        
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|   | b)                                                                                                                                                                                                                                                                                                        
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Date: June 24, 2005

/s/ Felipe Cerón