To assess the appropriate level of hybrid bond issuance for Naturgy Energy Group S.A., we examine the company's financial position as of December 31, 2022:

1.  **Financial Position and Leverage:**
    *   **Equity:** The company's total equity is 9,979 million EUR.
    *   **Debt:** The company carries substantial non-current financial liabilities (13,999 million EUR) and current financial liabilities (2,302 million EUR), totaling approximately 16,301 million EUR.
    *   **Total Adjusted Capital (Equity + Net Debt):** Approximately 26,280 million EUR.
    *   **Profitability:** EBITDA is strong at 4,954 million EUR. The company has shown solid cash flow from operating activities (4,242 million EUR).
    *   **Capital Needs:** Naturgy is an energy infrastructure provider facing significant transition-related capital expenditure. The "Property Plant And Equipment" grew from 16,587 million EUR to 17,379 million EUR year-over-year, indicating a sustained investment program.

2.  **Rationale for Hybrid Bonds:**
    *   Naturgy is a capital-intensive utility/energy company. While its EBITDA and cash flow generation are healthy, it carries a heavy debt burden relative to its equity base.
    *   Market conditions in 2022 saw a significant increase in interest rates (Swap Curve 10Y rose from 0.053% to 1.927%). Issuing traditional debt is becoming more expensive, and hybrid bonds offer a mechanism to bolster equity credit to maintain investment-grade ratings while managing the leverage ratio.
    *   The company does not have "very high" refinancing needs that would suggest a 15% allocation (the "do or die" scenario). However, given the energy transition requirements and the need to maintain a strong rating profile while managing interest costs, a moderate-to-significant optimization is appropriate.

3.  **Selection:**
    *   A 7.5% allocation fits the "moderate refinancing or acquisition needs" and "hybrid issuance meaningfully improves adjusted leverage metrics" criteria. It provides the necessary capital flexibility to support ongoing investments without the excessive cost burden or signaling risks associated with pushing toward the 15% regulatory cap. Given the current capital structure, a 7.5% target represents a balanced approach to maintaining rating headroom while funding strategic capex.

<answer>7.5%</answer>