I'll analyze ENI S.P.A.'s capital structure and determine the appropriate reliance on hybrid bonds.

## Key Financial Analysis

**Current Capital Structure:**
- Total Equity: €55.23B (2023-01-01)
- Long-term Borrowings: €19.37B
- Short-term Borrowings: €4.45B
- Current Portion of Long-term Borrowings: €3.10B
- Total Debt (excluding leases): ~€26.92B
- Lease Liabilities: €4.95B (current + non-current)

**Existing Hybrid Bond Activity:**
The company already has perpetual subordinated bonds (hybrid bonds):
- In FY2021, they issued €3.0B in perpetual subordinated bonds
- In FY2022, they issued €2.0B in perpetual subordinated bonds
- Coupon payments on perpetual subordinated bonds: €138M (FY2022), €61M (FY2021)
- These are recorded in "Other Reserves" under equity, consistent with hybrid bond treatment

**Profitability:**
- Net income: €13.89B (FY2022), very strong
- Operating profit: €17.51B
- Revenue: €132.5B
- Strong cash flow from operations: €17.46B

**Credit Profile:**
- Investment-grade company with strong cash generation
- Debt/Equity ratio: ~0.49x (moderate leverage)
- Significant retained earnings: €23.46B

**Market Conditions:**
- Rising swap curves in 2022 (5Y at 1.726%, 10Y at 1.927%)
- Corporate bond spreads (iShares Core Euro Corp Bond) at ~1.085%
- Sub-senior delta for non-financial IG is 0.2%, meaning the additional cost of subordinated vs senior debt is relatively modest

**Arguments for Hybrid Bonds:**
1. ENI already uses hybrid bonds (~€5B outstanding based on issuances), showing comfort with the instrument
2. Hybrid bonds receive 50% equity credit from rating agencies, helping maintain investment-grade ratings
3. The sub-senior delta is only 20bps, making the cost premium manageable
4. Strong profitability supports coupon payments
5. As a large energy company with cyclical earnings, hybrid bonds provide financial flexibility (coupon deferral option)

**Arguments against excessive reliance:**
1. The company has very strong equity (€55B) and doesn't need excessive leverage optimization
2. Rising interest rates make new issuances more expensive
3. Hybrid bonds are more expensive than senior debt
4. The company generates massive operating cash flows, reducing the need for complex financing

**Proportion Assessment:**
ENI has approximately €5B in hybrid bonds against total financing (debt + equity) of ~€82B. As a proportion of their debt capital, hybrids represent roughly 18-19% of total debt. Given their strong credit profile, existing usage of hybrids, moderate cost premium (20bps sub-senior delta), and the benefits of equity credit from rating agencies, a moderate allocation to hybrid bonds is appropriate. The company shouldn't rely entirely or heavily on hybrids, but a meaningful allocation of around 25% of their capital structure optimization makes sense given their existing practice and favorable conditions.

<answer>25%</answer>