I need to analyze whether Naturgy Energy Group should utilize hybrid bonds up to S&P's 15% equity credit cap on hybrids relative to total adjusted capital.

Let me consider several factors:

**1. Capital Structure Analysis**

Total Debt (2023-01-01):
- Long-term borrowings: €12,689M
- Current borrowings: €2,110M
- Lease liabilities (non-current): €1,309M
- Lease liabilities (current): €177M
- Total financial debt (excluding leases): ~€14,799M

Total Equity: €9,979M

Total adjusted capital (debt + equity) ≈ €14,799M + €9,979M ≈ €24,778M

15% cap = ~€3,717M in hybrid equity credit potential

**2. Leverage Considerations**
- Debt-to-equity ratio: ~14,799/9,979 ≈ 1.48x
- This is moderately leveraged for a utility company, but not excessively so.

**3. Interest Rate Environment**
- Swap rates rose significantly in 2022 (5Y went from -0.264% to 1.726%, 10Y from 0.053% to 1.927%)
- Corporate bond spreads also increased
- Higher rates make hybrid issuance more expensive, but hybrids can still provide cheaper equity-like capital than pure equity

**4. Credit Profile**
- EBITDA: €4,954M (2022), strong improvement from €3,529M
- Net income: €1,826M
- Operating cash flow: €4,242M (strong improvement from €1,001M)
- The company has solid cash generation

**5. Hybrid Bond Benefits for Utilities**
- Naturgy is a regulated utility with stable cash flows, making it a typical hybrid issuer
- Hybrids can improve credit metrics by receiving partial equity treatment
- Utilities commonly use hybrids to optimize their capital structure

**6. Existing Financial Position**
- The company has significant debt (~€14.8B) relative to equity (~€10B)
- Cash flow hedges show large negative OCI positions, suggesting commodity/interest rate exposure
- Strong EBITDA and operating cash flows support debt service
- Dividend payout is significant (€1.2/share declared + €0.5/share proposed)

**7. Assessment of Hybrid Utilization**
- The company's leverage is moderate for a utility but could benefit from hybrid equity credit
- Strong, stable cash flows from regulated/contracted utility operations support hybrid servicing
- The rising rate environment makes timing considerations important but doesn't preclude hybrid use
- Naturgy has a typical utility profile where hybrids are commonly used and well-received by the market
- However, the company already has reasonable leverage and strong cash flows, so it doesn't desperately need the full equity credit capacity

Given that Naturgy is a large European utility with:
- Moderate leverage that could benefit from some equity credit improvement
- Strong and improving cash flows
- A stable regulated business model well-suited for hybrid issuance
- Significant capex needs (€1,687M in PP&E/intangible purchases)
- Active dividend distributions

The company would benefit from utilizing hybrid bonds but doesn't need to maximize to the full cap. A moderate-to-high utilization makes sense - enough to meaningfully improve credit metrics while keeping hybrid costs manageable. Utilities like Naturgy commonly issue hybrids at around 50-75% of the S&P cap. Given the moderately leveraged position and strong cash flows, I'd estimate around 50-75% utilization. The leverage is not extreme for a utility, suggesting they don't need the maximum, but the benefits are clear enough to warrant significant utilization.

Given the balance of moderate leverage, strong utility fundamentals, and the beneficial but not critical need for equity credit, I'd lean toward 50% utilization.

<answer>50%</answer>