Let’s reason step-by-step.

**1. Company context**  
ENI S.p.A. is a large Italian energy company. From the data, we can see:

- It has significant property, plant, and equipment (€56.3bn in 2022, €56.3bn in 2021), typical of a capital-intensive industry.
- Revenue is very large and volatile due to commodity prices (€132.5bn in 2022 vs €76.6bn in 2021 and €44.0bn in 2020).
- Profitability swings widely: from -€8.6bn in 2020 to €13.9bn in 2022.
- Financial leverage is significant: total liabilities €96.9bn, equity €55.2bn, a Debt/Equity of about 1.75x.
- Operating cash flows are strong but variable.

**2. Hybrid bonds characteristics**  
Hybrid bonds have equity-like features (subordination, coupon deferral) and are treated partly as equity by rating agencies. They are most suitable for:
- Investment-grade companies
- Capital-intensive industries with stable or predictable cash flows
- Firms wanting to protect their credit rating while raising capital

**3. ENI’s situation**  
- Its earnings are highly cyclical (oil & gas price exposure).
- Heavy reliance on hybrid bonds could increase financial risk if commodity prices fall sharply (2020 loss was massive).
- Hybrids usually carry higher coupons than senior debt, so if cash flows are volatile, fixed obligations can become burdensome.
- A moderate use (e.g., up to ~25% of total capital structure) could be justified to optimize the cost of capital without endangering rating thresholds or liquidity.

**4. Conclusions**  
Given ENI’s credit profile, volatility, and existing debt levels, a limited reliance on hybrids seems prudent. Moving to 50% or above would be too risky for such a cyclical business. Pure equity or pure debt extremes are unsuitable.

<answer>25%</answer>